512 meg of ram is Windoze 95 specs! Wow, dark ages! XP should have a MINIMUM of 1gig if you want to do anything other than look at the pretty XP eye candy.
I found moving my home system from 1 to 2 gig was a big improvment. Even WEB browsing sped up, amazing enough, but like Bill the Gates himself said on a televised speech a few years ago "web browsing take more horsepower than anything else we do today".
Granted, that was at least 6 or 7 years or so ago, it's still pretty true. If I want to KILL my PC totally, open a few instances of any browser and hit eBay and a few sites like that - then check the processes using the most memory..........
Be that as it may, I'd not let your basic secretary limp along on 512 meg today. Besides, memory is pretty cheap in this day and age, compared to how it used to be............
I know from experience - my notebook is XP with 512 meg ram and there are evenings when I'm ready to totally toss it right through the big window sitting next to me and not even open the window first, it's so infuriatingly slow.