Can I use graphics cards

I have a computer which has 1 GB RAM, Pentium Dual Core and have PCI slot. I want to buy a graphics card, but when I ask my friends, they say I can't have a graphics card. Because graphics cards for PCI slot is not available today. I want some ones advice, Is this true ? Can you suggest me good graphics card ( 256-512 Mb ).
And its Indian price. If I cant have one, can you suggest me what I have to do for this problem.
