clearly the CPu is bottlenecking performance, but aside from that the only way your gonna bopst ingame performance is by using the best availabe drivers and disabling many of windows pretty features....run win7 basic profile instead of aero for example, and turning off any background tasks you don't need to free up ram.
You may find adding more ram is the simplest fix for the issues, personally gaming on less than 2gb on vista/win7 is going to be twitchy.