I was about to buy myself a geforce 8800GTS a then wondered if a pentium 4 670 3.8ghz would run it well
Erm, not really, upgrade to a C2D and then get the 8800, that'll get you bigger performance increases. Also, please can you edit posts, not double post? It makes it easier to read that way.
a 3.8Ghz would run fine with the card no need to upgrade, if your only focus in life is to run 3dmark at 1024x768 or whatever then yes you'll need a better CPU to see higher frame rates and scores but if you actually use your machine for games and want a smooth frame rate backed up with good image quality etc. then any sort of high power CPU will do the business, a 3.8Ghz P4 may not be as powerful as an X2 or C2D but its good enough for games especially when backed up with a decent GPU like the 8800, if you already have a highend GPU its probably ddebatable whether its worth it, what are yuor specs at the mo.
also what do you think of this motherboard ECS - RS400A - INTEL MOTHERBOARD or should i get something a little better