Microsoft has released a "refresh" of Release Candidate 2 of Service Pack 3 for Windows XP. This is another way of saying it is still in Beta. The folks at Microsoft indicated that the final version of SP3 will be available by July, but have not yet set a firm date. They are waiting on customer feedback about the Beta versions.
You can download SP3-RC2 if you want to be a Beta-tester, but I would not recommend it on a computer that you need to depend on for everyday use. You can find it on the Microsoft download site.
Vista SP1 Released
Microsoft released Service Pack 1 for Vista for public download/installation last week. It is generally recommended that users apply this update, BUT, I recommend that you let it run in the wild for a month or so before installing it. Watch the news, and listen to feedback from other users who have installed it first. Microsoft has a track record of having "gotchas" in its first service packs for its new Operating Systems.
There are news reports that some Vista computers cannot successfully complete the SP1 update due to device driver problems. (There are several other causes of the SP1 update failure, but most of them seem unlikely.) Here is a link to Microsoft's site pertaining to the SP1 update failure.