Scroll & Window lag

I've just downgraded from Windows 7 as it wasn't running very smooth. This has happened to me several times before when I've tried to re-install XP on my other PC, and this one.

It's basically when I try to scroll, or move a window, it basically drags like a wave. It takes forever, and is VERY annoying. I'm also using a AGP - PCI adapter if that means anything, I've tried downloading several video card drivers and they're not working, I just uninstalled all of them.

AMD Athlon XP 3200+
2.21 GHZ, 1.50 RAM.
Sapphire HD 3650 512MB DDR2 PCI-E.