And don’t worry, Twitter users: You won’t be getting come-ons for Vista in your Twitterstream. Not yet, at least.

The program that Twitter has rolled out today–something called ExecTweets–is a fairly cautious step into marketing, and that is certainly by design. But it does give a you a good sense of what Twitter thinks it can do with its buzzy, fast-growing and almost revenue-free product.

Today’s news: Microsoft (MSFT), via its Federated Media ad network/platform/agency, is sponsoring a page that collects Tweets from various executives. Twitter will get an undisclosed payment for giving the site its stamp of approval and for promoting the site on Twitter itself. Federated says it plans on launching similar programs on Twitter with other clients.

Soon, most likely today, Twitter users will start seeing promotions for ExecTweet on the main Twitter login page, and in the little box that Twitter just started featuring on profile pages. The one that looks like this:

As advertising goes, this is pretty innocuous. Hard to imagine even Twitter’s most anti-advertising adherents having a big problem with this one. But it’s also hard to imagine that many people will see the ads at all since the majority of Twitter use happens off the site, on mobile apps like Twitterific for Apple’s (AAPL) iPhone and desktop clients like Tweetdeck.

And it’s hard to imagine that many folks will want to use ExecTweet, period: The whole joy of Twitter is seeking out and finding specific people you find interesting–not just a mass of people whose common thread is that they’re “executives.”

I already follow AOL founder @stevecase, for instance, who’s prominently featured on ExecTweet right now. But I don’t imagine I’ll want to pay attention to others who show up on ExecTweet simply because they’re on ExecTweet.

And note that nothing about ExecTweet required Twitter’s OK: The company’s open API model allows users to repurpose its data for their own Twitter apps, and countless entrepreneurs and engineers are doing just that.

But there is something to be said for branding campaigns launched with Twitter’s approval and participation. Figuring out exactly how much that will be worth, and what it will eventually look like, will likely take Twitter and its ad partners a while to figure out. But now they’re starting. Finally.

TweetDeck, a one-man company that makes a very helpful piece of free software that organizes your Twitter streams, is raising an angel round led by Betaworks, the investment company with a hankering for all things Twitter. The round, which hasn’t closed yet, will eventually end up somewhere south of $500,000, I’m told.

When it does, the financing will make 34-year-old programmer Iain Dodsworth a paper millionaire. Nice work for a Brit who built TweetDeck just last June because he was following 30 people on Twitter and wanted a better way to organize their Tweets.

Dodsworth says TweetDeck has been downloaded 250,000 times since then and that users are sending out 120,000 messages a day using the software. That places it above other free Twitter clients like Twitterific and twhirl, both of which are cranking out 80,000 to 85,000 messages a day, according to tracking service TweetRush.

All of them are part of the burgeoning ecosystem that revolves around Twitter, which powers all of their companies by letting them plug into its data stream. In exchange, all of these companies make Twitter more successful, by bolting on frills and features to its bare-bones service.

And no money changes hands at any point: Twitter doesn’t charge for use of its data, and its partners do all their development work for free. That could change at some point. As Twitter casts about for a business model to support its service–it is, famously, just about revenue-free at this point–an obvious solution would be to start charging a fee to the likes of TweetDeck.

No problem, says Dodsworth, who says he’d be happy to pay Twitter, particularly if it gave him even more access in exchange. Oh. And what about his business model? It’s coming, Dodsworth says–he’d like to start selling a pro version of his software, targeting power users and corporations.

That strikes me as a fairly small market, but then again TweetDeck is a very small operation. Dodsworth says he doesn’t plan on hiring any additional help in the near future, even as he preps new features like a version for Apple’s (AAPL) iPhone.

I’ll let him explain himself, via a short video interview I taped with him yesterday–just as soon as the Internet cooperates and lets me post the clip. In the meantime, you can also track Dodsworth on Twitter here or here.