i play on xp. but i have a desktop which is much more powerful than yours and i run out of memory... my skype will crash if i attempt to voice chat with someone and play haven. i think haven by itself will take 700mb of memory.... i dont think 1g of ram is enough.
if you truley cant buy a new computer, maybe see if you can increase your ram somehow? however i doubt you can play with an older onboards graphics card.... that eats up ram to.