I just checked TODAY on ram prices, ddr2 800 2x 1gig chips is 85 bucks from wintec, and other brands aren't far behind on the price point... eg corsair if you want brand name. honestly I just figure ram is going to be what suits your system the best, not the price, because it's all so inexpensive now.... unless you're running Shista (vista) it's not likley that you'll need more than 2 gigs of ram... especially if you're running an os like ubuntu, linux or anything like that. they eat less resources then even xp. and from personal experience run faster and more smoothly. (dual boot direct comparison xp x64 vs. ubuntu x64)
ps. if you hit up a socket am2 system you should be able to upgrade for a while, i think they're still putting the "phenom" or four core procs on the socket am2... I'm not sure about all that stuff on the intel side... i DO know however that amd is going to cost a little less, and will handle larger instruction sets much more smoothly than intel... intel will run small instruction sets faster than amd's, so i mean, games and photoshop and all that jazz, i'd definitly get an amd... cuz unless you're running 200 instances of programs like aim, gaim, pidgin, fifty browswers... even so, you won't notice a big difference in the small programs anyway... however when you do need your proc to crunch the big numbers as in 3ds max you'll notice faster render times and what no (on amd)t. (not my opinion, test charts and what not stated, i read way too much). unless you're going for a huge tweak system, i'd just hit the amd... save some dough, you wouldn't notice the difference either way for the most part on standard os/operating system/games and what not... i mean, if you're a freak about the numbers, than read some of the charts for systems similar to the ones you've mentioned. But if you just want somthing that saves you some dough, and kicks all the wait time out of the way, again... AMD.
ps. last time i checked you can hit up a 320 gig hd for less than 95 bucks, i think newegg had some decent ones for around 75 or so (oh, and the chache size hardly affects the performance as noted in a review on tomshardware) and a 2.4ghz amd is floating around 100 bones on newegg for the socket am2.