are the games that say games for windows only playable for window vista?

no...Games for Windows games are not only for Vista....

right now the only Vista only games are Halo 2 and Shadorun...the rest are on XP too.

cause i wanna buy halo 2 and lost planetsly718

It depends. You need to look at the System Requirements on the back of the box, and it should say which Operating Systems it runs off of. Unfortunately, Halo 2 is only for Vista, but thankfully Gears of War is coming out for XP.