Your first consideration is what type of card fits your motherboard. I suspect you have a PCI Express slot, as opposed to AGP. Looks like there is a new PCI Express 2.0, but you might want the older PCI Express 1.1. 

Once you determine that, you choose from that type of card for the performance you want.

In addition to the performance specs of the card, you should consider how much power the card requires vs the output of your computer's power supply. 

Next you could think about the heat generated by the card, and how it will be cooled. Some are cooled by (noisy) fans and some are passively cooled by heatsinks (no noise). In general, higher performing cards probably use more power and generate more heat.

Tom's Hardware and the Guru of 3D are good places to research video cards.

http://www.tomshardware.com/reviews/Components,1/Graphics-Cards,4/
http://www.guru3d.com/index.php?page=review


>From: Melani Gump <[log in to unmask]>
>Subject: Re: [PCBUILD] Video Cards
>
>  Hi,
>I have a Dell Dimension 5100.  I was wanting to know what a really good (and
>cheap) graphics card would be that is compatible to my computer.  I would
>like at least 512MB in ram and at least 6800 GT.  
>
>
>
>Can you help?
>
>
>
>Thank you, 
>
>
>
>Melani
>
>            Do you want to signoff PCBUILD or just change to
>                    Digest mode - visit our web site:
>                   http://freepctech.com/pcbuild.shtml
>

               The NOSPIN Group Promotions is now offering
                 our special coffee mugs and mouse pads
              with the PCBUILD logo...  at a great price!!!
             http://freepctech.com/goodies/promotions.shtml