Upping to a P4 will probably require a new case and powersupply, along with MB. Video card upgrading is tempting, but not if you plan to re-upgrade in a year, because you can either spend a few hundred on a good vid card now, but then it\'ll be behind your system next year, or a lot more, for cutting edge (which\'ll be good enough in a year), but that\'s big money.
Raid... what I mean is you buy, say, two 80 gig HDDs, and set them up so the computer uses them as 1 160 gig hdd (that runs 2x as fast, or 3 80s as 240 3x as fast, etc...). I did that with my system now, and it\'s pretty sweet, and it\'s the kind of thing you can take with you to a new system.
Heat\'s right though, your MB may not have hardware support for RAID setups (which modern MBs usually do), so that would depend on ur MB.
Either way, my advice is to buy one (or two) big HDDs that will be just as usefull to your computer next year.