|"I dont want to buy graphic card..."|
More than likely, that is the ONLY solution. You didn't list which graphics "card" you currently have, but I suspect it's onboard graphics (built into motherboard) & not a card at all. You could also use more RAM. 1GB is the minimum for Win7. It will perform much better with 2GB or more.
If you need help selecting a card, let us know. This article should help:
Best Graphics Cards For The Money: May 2011