I put together this system in January, I had a few minor troubles with Win95OSR2.1, but Win98SE runs great.
My roommate put together a very sismilar system and he's had a problem with his cheap assed soundcard in WinME, but it's an Ensoniq 64 PCI and they are known for being picky about drivers.
We also put together a 3rd machine that is almost exactly like mine but with a G400 instead of a Voodoo3 and a 27Gig maxtor HDD, and the guy hasn't complained once. And he would...be was one of those picky people that b1tched about the 2D quality on a TNT...
Just so you know me and my roommate both have our same 250Watt PSUs we had before, and we both had our plain generic RAM (i upgraded to Micron RAM cuz I got it at cost difference between my old RAM) and that was even fine.
Tthe MSi K7T Pro is near flawless from what I've read go for it for non-OC stability, and if you want multiplier adjustments try ABit KT7, it's nicer to be able to adjust in the BIOS rather than with jumpers/dips
Anandtech uses Thunderbirds on MSi K7T Pros for their webservers. If it's good enough for AT's servers, it's good enough for me
Edit: Just to make that clear, I have never personally used a K7TPro, but reading reviews from Anand and others people are very impressed with most of MSi's new boards, the K7T Pro and Master among them.