http://www.crucial.com/store/listpar...=Pavilion+374n
I suggest the 1 GB module.
Using On-board graphics with games will provide you with poor performance. Linux uses OpenGL which is very dependent on video RAM capacity, video RAM bandwidth, and raw GPU/VPU speed. On-board graphics fights bandwidth with the main processor and usually the shared memory is small.
Buying desktop computers from brands like Dell, HP/Compaq, Gateway, and many others are ok for farmer john like people, but it is best to build the computer when it is going to be used for games.