I'd like to replace it with a stronger card, however my medium footprint case can't handle a card over 8 inches, it won't fit. Would any have any recommendations?
Also, I only have a dell factory stock 305p/s (which is upgradeable but I've heard dell 305's can handle cards requiring upto 350power). I'm further concerned that my outdated 3800+ cpu may bottleneck any stronger card.
That PSU is very weak, you will need a new one. Your CPU will definitely be a bottleneck, so you will probably want a new one also.
Have you considered just building a whole new computer? Since you need all these new parts anyway, I'd say thats a good idea. You could even use some parts from your dell to help you save some cash (Hard drive and any CD/DVD drives would probably work ok)