If you want to change your video card, you have a lot of choices. The following cards will work in your Cube ( you may need to change the faceplate of the card, or make a custom one.) :
Radeon
Radeon 7500
GeForce2 Mx 32 Megs
GeForce 2Mx 64 Megs
Geforce 2Mx Twinview (you need to design a custom faceplate)
GeForce 3