I'd just upgrade the RAM, it is somewhat universally beneficial. Graphics card wouldn't bother.
Worth checking if the board can support higher, like PC3200/DDR400, since with some CPUs that can be a bit of a botteneck so if you can eliminate it now while your at it, it is all good. Would also check if dual channel mode is supported, as you could say.. sell the 512MB in there now and get a 1GB kit.