that machine would make it rather difficult to do video work!
its an older dell, so upgrades could prove difficult if not impossible. they like to use some propietary stuff, so you have to buy from them for upgrades.
take a look at the dell site, see what the possibilities are.
all that said, your best bang for the buck will be with more ram. 512 is the minimum I would want to run XP with and do anything processor intensive. things like video which are moving large amounts of data around would benefit greatly from 1 or 2 gigs of system ram. if that machine can handle it...
the video card is pretty old as well, an upgrade to that would help-again, assuming you can.
ram would be my strongest suggestion, followed by video.
also consider that yours is a fairly old machine, so how much money do you want to dump into beefing it up, compared to getting a new machine- store bought or build yourself, you can get an incredible upgrade to that system, in the $600-700 range.