I'm using XP with Logic Audio and it works fine so far. XP is a faster OS than 98. In theory the features of the OS should make it a better fit for audio than Windows 98. However, there is s difference between theory and reality. The thing is most DAW related companies that make products for PCs have been writing Windows 98 drivers forever, but NT is new to them. So there's growing pains involved for many companies.
For example, two e-magic products that I use, SoundDiver and Unitor control for my MIDI interface both suffer from XP related problems. When I first encountered the problems, I immediately went to the e-magic web site figuring any reputable company would post info and a fix, but couldn't find the answer (even though they know of the problem and the workaround, I guess they have a different view of customer support than I do). So I spent a couple hours doing web searches to find an e-mail list archives where an e-magic rep hangs out. Turns out all I had to do to work around the problems is set the MIDI buffer size to 1K, which worked great, but there was some aggravation getting to that point where I had a fix.
Thats the kind of thing I'd expect when it comes to XP. It will be a while before most companies catch up and have XP support comparable to that for Windows 98.