Dual monitors causing big problems

I've just installed a second graphics card so that I can extend my desktop across two monitors. After configuring everything correctly in Display Properties (setting the resolution of the two monitors, indicating which one was on the left and which on the right) my computer started having issues. I couldn't get Display Properties open again (I had to pull out the second graphics card to get it open again--with both cards in trying to access that control panel would get me a blue error screen). Also, IE would freeze frequently, right-clicking on the desktop could cause a freeze. My system is as follows:

AMD Athlon 1GHz, 128MB RAM
Windows ME (upgrading to 2000 or XP soon . . .)
original video card is some sort of older NVIDIA AGP card

The card I added is a cheap "Jaton" brand card with a "Trident Blade T16" chipset.

Any advice would be greatly appreciated.