IMHO an upgrade from integrated to dedicated graphics is always a good if not necessary investment when you're wanting to actually play games on your system. Games tend to lag up bad on systems with even the best integrated graphics, mostly because during game play both the central processor and the graphics processor are trying to use the same memory. The battery upgrade would be nice but I would consider it to be more optional than the graphics upgrade. What I would spring for instead of the battery upgrade is a memory upgrade to 4GB as you won't be able to utilize dual channel with 3GB and that will affect your system performance significantly.
I am thinking of buying the Dell inspiron 1545. It has a Intel core 2 duo T6500 processor, 3GB memory and 250GB hard drive. I want to use the computer for Univeristy work and general surfing but would like to play the occasional game like The Sims of Monkey Island. Should I pay the extra