First off let it be known, that like you tommyb10 I am an owner of an old Dell Dimension 3000! I got the unit several years back at a local garage sale. After about a year of use, I wanted to upgrade the graphics, for the on-board video adapter off the motherboard just wasn't cutting it.
The Dell 3000 is a tricky beast, when it come to upgrading a graphics card, for mine is (old school) and only accepts PCI slot card, not PCI-(Express), nope strictly PCI only. So that makes is hard when it comes to verity when shopping for a card.
After a couple days for hunting around, I came upon a "used computer components" store here in my town. Went in and shopped around, and came upon a decent looking little card, it was a Nvidia 5500 256MB PCI card!
The following link will give you some information about the card....
http://www.amazon.com/Nvidia-Geforce-FX5500-128-bit-TV-Out/dp/B0042A3LQY
While at that "used components" store the guy behind the counter told me that it might be a good idea to upgrade my power supply to at least 300 watts, for he told me the card has a considerable power draw vs. on-board video and with my Dell 3000 coming stock with a small 250 watt power supply, he told why push it and take a chance. So I purchased a used 450 watt power supply that would fit the old Dell 3000 case. I would recommend you upgrading your power supply to at least 300 watt or more.
I got myself a used Raidmax RX-450K 450W ATX12V Power Supply, for around $12.00......
http://www.google.com/products/cata...X&ei=ojKrTe71NurdiALW28jvDA&ved=0CKEBEPMCMAQ#
I know there are better PCI slot only video card out there on the market, but the one I got just works so darn good. I really do like my card, no matter how (old school) it is.
Looking forward to hearing what you decided to go with!