A nice little bit of back-to-school marketing for Apple (AAPL), which likely has an eye trained on education sales as the new school year begins.

Later this afternoon, BoomTown will be front and center–well, I will probably get seated on the far side and way back–for a speech to be delivered by Microsoft CEO Steve Ballmer at Stanford University’s Memorial Auditorium on innovation and entrepreneurship. Part of the Entrepreneurial Thought Leaders Seminar, it is aimed at students there who are looking for some advice from tech’s big dogs.

Ballmer is, of course, all that, with a blustery bark and an occasional bite.

Of course, he’s probably channeling a more charming demeanor in another meeting sources say he plans to have with Yahoo CEO Carol Bartz on this visit to Silicon Valley.

The second since Bartz took over Yahoo in January, it’s about whether or not the pair should make nice after a long period of useless acrimony, and strike a significant search and advertising partnership.

Many close to the discussions, which have been going on seriously since late March between small teams from both companies, said that how the pair get along and whether they can actually pull the trigger together is all that matters.

Rapport is key, especially since such a deal has been exceedingly complex to figure out.

The latest idea is one in which Yahoo (YHOO) would take over both search and display advertising sales and Microsoft (MSFT) would run the tech for both behind the scenes.

It’s not clear if trading other assets–-such as content–-or a large investment in Yahoo by Microsoft are being considered too.

If struck, such a deal would be a major shift for both companies in their business focus and would also tether them tightly together to better compete with Google (GOOG), which overwhelmingly dominates the lucrative search market.

Still, sources said, there is a lot keeping Microsoft and Yahoo apart, most especially a profound wariness over controlling key technologies and tense history between them.

In addition, execs on both sides–such as Microsoft digital head and former Yahoo tech exec Qi Lu–are treading carefully about every item, unsure of how so many ties would be handled.

“Could we fire Microsoft if they did not perform?” asked one Yahoo exec. “Or would we be stuck without control over our destiny, if it all went south?”

For her part, sources who have spoken to Bartz about the recent discussions with Microsoft said, she has remained resolute in not giving up too much power to Microsoft.

Microsoft is also gun-shy after its disastrous takeover attempt of Yahoo failed last year–with Ballmer loath to make another such epic mistake in trying to turn around the software giant’s lackluster digital efforts.

“He simply does not want to look stupid again,” said one Microsoft source. “So it weighs on whether he has the guts to put himself out there.”

That’s ironic, of course, since his Stanford speech today is on entrepreneurialism and innovation, which always require an ability to use failure as a way to move forward.

The question is, can Ballmer walk that talk?

Recently, BoomTown reported that talks between Microsoft and Yahoo had gotten “hot and heavy.”

That mood seems to be continuing, as many sources close to the situation on both sides said that the pair are coming ever closer to a search and advertising partnership deal.

Said one source: “It’s closer than it has ever been…we’re finally talking about the how rather than the if.”

“It’s meaningful,” added another source. “The fact that there is even progress and engagement, after so many failed attempts between us, says a lot.”

Indeed, it remains a good sign that there seems to be a lot of engagement between the two sides of late, and some sources think a deal could even be struck within the next few weeks.

As I also reported last week, the latest idea is one in which Yahoo (YHOO) would take over both search and display advertising sales and Microsoft (MSFT) would run the tech for both behind the scenes.

It’s not clear if trading other assets–such as content–or an investment in Yahoo by Microsoft are being considered too.

In any case, any such deal would be a major shift for both companies in their business focus and would also tether them tightly together.

Many think they need to be tethered, given that Google (GOOG) overwhelmingly dominates the lucrative search market. Yahoo is strong in display, although that market has been harder hit in the recent economic downturn.

But whether or not Yahoo and Microsoft can come to a partnership agreement–given the deep complexities of the situation, the wariness over controlling key technologies and tense history between them–is a big if, of course.

Still, sources on both sides seem more positive than ever before.

Microsoft execs, for their part, report that new Yahoo CEO Carol Bartz is much more straightforward to work with than former CEO Jerry Yang.

And Yahoo’s side seems convinced that Microsoft appears more willing to make a deal happen and is more flexible on terms than in previous encounters.

Both sides are using very small teams to discuss the possible partnership, mostly in Silicon Valley. Some of the Redmond, Wash.-based Microsoft team, in fact, are in the Bay area now.

Sources said those involved on the Microsoft side include: Digital head Qi Lu, a former Yahoo tech star; top M&A and strategy exec Charles Songhurst; Online Audience Business SVP Yusuf Mehdi; and several others.

On the Yahoo side: North America EVP Hilary Schneider, who leads the efforts; General Counsel Michael Callahan; top Yahoo ad operations techie Mark Morrissey, who was key to its revival of the Panama ad system and has recently been leading product development on its new ad platform; finance SVP and Chief Treasury Officer Mike Gupta; and Products EVP and CTO Ari Balogh, although he is more in the background.

Of course, the only two execs who will matter, if these teams finally manage to hash out details, are Yahoo’s Bartz and Microsoft CEO Steve Ballmer, as well the both companies’ boards.

Interestingly, Ballmer is slated to be at Stanford University’s Memorial Auditorium to give a lecture on innovation and entrepreneurship as part of the Entrepreneurial Thought Leaders Seminar on Wednesday afternoon.

Whether Ballmer is seeing Bartz on this trip or not is not clear.

But he has to at some point. The approval of a deal–which could be struck soon, if terms can be reached–will be entirely their call.

[Postcard image courtesy of CarbonClothing on Zazzle.com.]