I wnat to upgrade my windows xp for free.?

I want everything upgrade,drivers etc. I'm also getting Unreal Tournament 3 for the pc so i want my computer to be upgraded to handle that, i want to have nice experience with ut3, i actuall want to notice the awesome graphics without loweing the detail. But it isn't just about ut3, i want my computer to be up to date. Is it posssible ican just download all of this stuff off of the internet for free. Please tell and give me some helpful links.