How can i play resident evil 5 on higher settings?

i have got resident evil 5 on my pc.it lags on medium or higher settings.it works in low settings but looks really crap.my specs are 4 GB DDR3 ram,3 GHZ dual core processor,1 GB radeon hd 4350 gpu and windows xp.i have already stopped every working process and use game booster.i also defragment my disk regularly so give some other solutions.thanks in advance for any responses.