your above minimum spec but only just.. with them settings and spec you should be able to play at @ medium setting dx9 if dx10 is enabled as the default you will need to make it dx9 (in the beta you cant or at least i havent looked) but in the full version you may be allowed to adjust the config files like on BFBC2 the 88gt is a great dx9 card probably the best but it was too weak to run dx10 propperly... so stick to dx9 settings on all your games and you may be able to up the over all quality and still have playable fps.
also i also suffer massive fps drops on caspian (see below for my specs) ... i went from a solid 60 to 7... i thought it was just the server but it may be the game itself. it certainly didnt do this on metro. but then again i installed the latest driver for my card, ment to fix both rage and bf3.
it did fix rage i havent tried bf3 metro yet but caspian seems even more broke.