agree - with XP you donīt need 2GB, even with onboard graphics. But I wish 4 GB for me, from this I could use 2 GB as RAM-Disk for Timeshifting, without Harddrive usage (Noise, fragmentation etc). Solide state discs are too expensive still.
But the predecessor of the 780G (the 690G/x1250) has serious driver issues with XP, which are still not solved after months.
ATI 690G/x1250 problems
I own one and this made me switch from XP to Vista. It would not surprise me if your new 780G will have same problems... And the release of this chipset is postponed already because of driver issues... I wish you good luck. If you have good luck, I will do a MoBo upgrade to 790G myself also (and XP downgrade at the same time?).
Donīt underestimate the improvements of Vista against XP in Multimediasupport.
There are reports that HD-Playback works optimal only with Vista (mainly because of EVR with DXVA 2.0 support). Under XP EVR with DXVA 2.0 is not possible. I could not get 1080i HDTV playback fluid with XP, but very easily with Vista.