i recently upgraded the RAM from 2gb to 4 gb on my asus a24f dual core system.. and the integrated HD had a significant jump from 758mb to 1558mb..
so i gues it does make a difference to beef up the ram... i used two 2gb cards in the two alloted ram slots..
The onboard video sub-system uses memory from the available RAM pool, reducing the total amount of memory available to the the OS to run programs and store data.
If your machine is running a 32 bit version of Windows, the OS can access is a little over 3 GB of RAM, max, but the video system can access RAM outside of that limit. You know this is true because you can display a boot screen (BIOS, etc.) before the machine even knows it has a hard drive, let alone an OS. Therefore, bumping your machine to 4 GB of RAM provies the video system with a RAM pool above the 3.x GB used by the OS.
I know this works because that's how I run my Compaq laptop with XP Pro. The BIOS shows 4096 GB of RAM, but from the desktop, Windows reports 3 GB available to the system.
The same would hold true under a 64 bit OS, except that the OS, itself, would not be limited to 3.x GB of RAM. In any case, more is better.