Horatio is correct, my thinking is to be sure you've got your C: drive formatted properly, use the format tool from the Win98 startup floppy, rather than PM.

On the power supply, AMD's minimum recommendation for the XP chip is 300W, so you're right on that minimum. Most people are more comfortable with 400, because the XP takes a lot of current. It's extremely easy to replace the power supply, it's just held in with 4 screws that you access from the back outside of the case. They're not symmetrical, so you can only put it in one way. If you want to get a larger one, I found this link for a page with Antec's PP-403X

http://www.provantage.com/FP_08853.HTM

That would be a nice ps for you, and you wouldn't have to worry about it down the road. I've never shopped there, but it looks kind of interesting, I'm going to look at it further myself for future reference. I'm a little leery of the power supply you've got because they don't give any specs on it, and they call it a 320, but then have no 320 available in their ps section. I think they're hedging the rating a little bit, so I don't really trust it.

Gainward makes good stuff, there's nothing wrong with your card. Like Horatio said it just need to be reinserted. But still, I know you've done it a few times, but getting a new 400W power supply, using the startup disk to format your boot drive and starting over from there sounds like the best bet to me.