Hi Saphired,
The GeForce 320m in the previous-gen MacBook Pro was roughly equivalent to the 9600m GS (perhaps slightly weaker - the 320m was definitely weaker than the DDR3 9600m GT). The 320m is a shared-memory IGP, so it has a little less memory bandwidth than the 9600m GS, but has 16 more pixel shaders (it shares the same core architecture with the 330m discreet piece). Depending on what you are trying to do with it, the HD 3000 is somewhat weaker than the 320m. Many have reported that the HD 3000 gives better frame-rates than the 320m on some games at low settings; this is due to the better processor it is paired with. As resolution and complexity increase the 320m pulls away from the HD 3000, even when paired with the slower C2D.
The bottom line is that the 320m IGP is no gaming monster and the HD 3000 is even weaker. Both will play a number of popular game titles at low to medium settings, but neither would represent an increase in performance over your current 9600, and the HD 3000 would represent a definite step backwards, in terms of raw GPU performance. CPU-intensive games may play better at low settings than your current setup, since the HD 3000 is paired with an i5 or i7.
If games are important to you and you must upgrade during the current revision, I would go for the high-end 15-inch MBP (as the AMD piece in the low-end 15 wouldn't be much of an improvement over what you have).