Vista - ATI Mobility X1700 in Asus Notebook troubles when playing games

I have an F3JP Asus notebook with an X1700 ATI mobility video card. Vista
seems to have DX10 pre-installed but the card is a DX9 card if im not
mistaken. Is Vista / DX10 automatically compatabile with DX9 or will I need
to somehow download and install DX9 ?
The reason I am asking is twofold, firstly :

Notebook gpu seems to be overheating after about ten to twenty minutes of
playing any 3d type game from WOW to Half Life 2 to the latest Unreal
Tournament demo. Graphics go fuzzy and the notebook locks up.

Secondly, Wow performs poorly, with ALL graphics settings taken to the
lowest possible I still only get 10-15fps while I still manage some decent
rates with the latest UT demo, I find this hard to fathom.

Has anyone got any ideas why this is happening? ASUS have not even bothered
to reply to me.