Here are a few questions about computers I’ve received recently from people like you, and my answers. I have edited and restated the questions a bit, for readability.

In last week’s Mailbox, you said that Windows XP machines can slow down over time unless you do “a lot of techie maintenance.” What did you mean? I regularly defragment the hard disk, tweak the registry, and clean out temporary files, but my PC is still slow.

All of these things are helpful, though I don’t recommend that nontechie users “tweak” the Windows registry, which contains vital program information that can mistakenly be removed or altered if you don’t know what you’re doing. Another speed-enhancing tactic is to use a program like Startup Cop Pro (snipurl.com/b4v91) to prevent unneeded programs from running at startup, and one like PC Decrapifier (pcdecrapifier.com) to clean out craplets — unwanted pre-installed programs.

However, what I had in mind when I wrote that was something more drastic, something a number of techies I know do annually: a complete replacement of Windows. This involves first backing up all your files, and then performing what’s called a “clean install” of Windows XP that wipes out everything on the PC and starts fresh. You then would copy back all your data files and re-install your programs.

This can make the computer feel like new, but the problem is that it can be tricky and tedious for nontechie users. Depending on the source of the copy of Windows XP you are using for the clean install, you may have to locate and re-install drivers for peripheral hardware and for hardware features of your particular make and model of PC. You may run into licensing and activation issues with your re-installed programs. And you may have to download numerous patches and upgrades for Windows itself and for your programs.

I am considering buying one of the new MacBook Pro 15″ laptops. What do you think of the keyboard on this laptop? Is it easy to type on compared to other laptop keyboards? What do you think of the shiny screen?

Because keyboard and screen preferences vary from person to person, I strongly urge all laptop shoppers to try out models they are considering before buying, even if only for a few minutes at a retail store. Having said that, I find the MacBook Pro keyboard to be very comfortable and easy to use, with good key spacing and feel. I personally prefer matte screens to glossy ones, but own laptops with both types and find the glossy ones acceptable, if not optimal.

I use the Windows Mail program that came with Vista on my computer. You say Windows 7 won’t come with that program. Is there something similar that can be installed?

Microsoft will encourage people to download a similar free program called Windows Live Mail, which is closely tied to its Live online service. Or, you could switch to a competing email program, or rely on Web-based email.

You can find Mossberg’s Mailbox, and my other columns, online free of charge at the new All Things Digital Web site, http://walt.allthingsd.com.

In theory, anyway. In practice, things turned out a bit differently. Hours after the iPhone arrived at market, Apple’s and AT&T’s discussion boards lit up with complaints from frustrated customers who’d run afoul of the new activation process, which was quickly overwhelmed by the sheer volume of activation requests.

I was one of them. I purchased my phone at about 8 p.m. PDT Friday and attempted to activate it about an hour later, only to receive a “Your activation requires additional time to complete” message from AT&T. Which was a disappointment because without activation, the iPhone is useless for everything but emergency calls and playing “Itsy Bitsy Spider.” I checked email for a follow-up message from AT&T a few hours later. Nothing. I went to bed, figuring I’d find it in my inbox the following morning. Thing is, when I checked email the next day, there was no message. Worse, service to my old cellphone had been cut off. I called AT&T and after an hour or so on hold managed to get through to someone who promised to expedite my activation.

Lot of good that did. Long story short, I was without cell service until early last evening (and I was one of many). Now, granted, I was porting a number over from another provider. But 40-plus hours is a longish time to wait for activation.

That said, market researchers from PiperJaffray estimate that Apple sold a half-million iPhones between 6 p.m. Friday and 6 p.m. yesterday. So there were bound to be a few glitches, right? “The iPhone is undoubtedly the biggest thing to ever happen to a cellular industry,” an AT&T employee wrote in a post to Apple’s support forums. “Last night, hundreds of thousands of people purchased iPhones at the exact same time, rushed home and tried to activate their phones asap. What happened was a massive bombarding of activations to switches that generally don’t handle anything near last night’s load. Since the phones were sold at 6 p.m., everyone got home at about 7 p.m. and most likely overloaded the switches to the point of near exhaustion! It would be like 30,000 or so people throwing basketballs at one hoop and hoping to make it in! Theoretically, larger metropolitan areas would have more problems due to more switch activity. Granted, our switches in New York City are heavy duty, but there are no switches in existence designed to handle that kind of load, because with the exception of this weekend, there would never be that much activity.”