Sorry to hear about your misfortune, thieving bastards anyway!!!
Yeah, about all you can do is crank the ol P4 as far as you possible can. If you can find another gig of memory el cheapo that would definetly help too.
i bought this p4 with msi board and 1gb ram and that 500w psu and a 15" working crt monitor for $100. with a keyboard and mouse.....so it was a bargain for me.... i added a 500gb hdd and 4830 to it....
you are right about ddr3, better not spend on a ddr2. the only way i can go with is to overclock it....what do you think about this cpu cooler>??
I'd say ask in the overclocking section and/or google for an older guide.
If I were you I'd look for another similar speed 2x512MB kit on ebay. there should be some for not too much at all, esp since that's 667 you're using.
Then I'd look up the mobo. It being 775 should mean that it can take at least those Pentium D's, possibly even a dual core variant. I'd get that off of ebay too. Depending on how high it goes that may well be much more worth it over a cooler for overclocking.