I have a similar laptop that had 512 RAM also, two 256 sticks. I upgraded it to two 512 sticks giving me one gig of RAM and noticed a significant difference. I also upgraded the hard drive from 4200 rpm to a 5400 rpm hard drive. Those two changes made a big difference. Total cost, about 125.00.
Edit: I should have put in two 1 gig sticks of RAM and still might do that. I'm only hesitating because I may just buy a new machine.
Give Windows 7 Release Candidate a trial on your old laptop. It's available from Microsoft until August 15. I've seen websites devoted to people installing Win7 on tired old computers, so it can be done. If you're happy with the results, it can buy you time -- time for SP1 to get rid of the more egregious bugs.
Market Data 
Markets 
AI
