ok, i'm basing my info off http://support.dell.com/support/edoc...cs.htm#1101572
memory is usually the worst choke point on most machine builds outta places like dell. if you've got less than 512MB of RAM, you should add some RAM.
dell's website says the 4550's only take up to 512MB DIMMS and you have two slots, so I'd get this
for 1GB total for $115 (cheap!).
you have WAY too many options on the video card, but an important question is do you see yourself moving this card to a new system in the future, or are you just trying the get another year outta this box?
personally, I'd prolly just get this
for under 200 bux, which was a high-end card once-upon-a-time. it's a toy, too, with support for dual-monitors, cable TV, and all that whack shit you get with ATI's AIW cards.
whatever you do, make sure you get a card that uses 4X AGP interface, cuz that's the max your current motherboard should be able to handle.
for anything more, you'd be better off throwing together a barebones system to just replace your current machine, but that could be a little more than 600 bucks, depending on the quality of your components.