I've said it before, I'll say it again: Windows Vista chokes on 1GB of RAM. If you bought a budget desktop, here's your chance to double the memory--and improve system performance considerably--for just 10 bucks. TigerDirect has a Crucial 1GB desktop memory module for just $9.99 after a $10 mail-in rebate.
This is 533MHz DDR2 RAM, a.k.a. PC4200. Make sure your existing RAM operates at the same speed, otherwise you could see some flaky results. Crucial is pretty much tops when it comes to RAM; the stick comes with a lifetime warranty. The rebate deal is good through Feb. 24; each household qualifies for two, so you can stock up on a pair of modules if you're so inclined.