New Video Card Needed. Help!

My machine reboots randomly. After some of my newbie-level of
troubleshooting and lots of digging around in newsgroups, I've narrowed
the problem down to my NVidia GeForce MX-200. Either the
incompatability with Win XP everyone's talking about, or it's just
given it's best 4 years, or what, I don't know. But I'm going to
replace it and see. The place I'm buying from will buy it back in 30
days if I don't damage it, so I can at least try it.

I have an AGP 4x slot. I see some AGP 8x, 16x. What do these mean? Is
this how fast they'll work? I hear I would be better to get one that
has it's own coprocessor. All I care about is that it can handle the
typical refreshing of a screen full of thumbnails (like the Windows
Explorer in thumbnail view) without my having to wait 15-20 seconds for
it to finish, and to play my videos in full screen mode with zero
hesitation. Beyond that, I don't do shoot up games, I'm not producing
and editing porn (not for lack of trying.) From what I've seen I should
be able to get away without paying more than $80 - $100. Does that
sound about right?

I know I need as much on board video RAM as I can get, I know that AGP
is faster than PCI, and I guess I should stay clear of NVidia for this
machine.

Beyond that, or in addition to that, can anyone recommend a card in my
price range that'll do what I need?

Much appreciation to any feedback.

tod