Graphic card help?

I must say I don't really understand graphics cards. I see often on system requirements that you will need a GeForce XXXXX. What I understand is that GeForce is a make of graphics cards but what if you have a different make, how can you compare if your card is good enough. What makes a graphics card good? Is it just the memory size? Now I have a ATI Mobility Raedon X1300 Hypermemory 128Mb. Is this good or bad and why? Any other pointers to get me started?

Thanks

No thats not a particularly good card, but its not the worst.

Nvidia make the Geforce series, and if a game says you need card xxxx or better, you need a card with at least that number. The first x is the generation type number and the second one is how good it is.

As for comparing them, generally games say you need at least this GeForce card, or at least this ATI card. Have another look, there should be two recommendations. Otherwise just google the cards and find some comparisons.