Well I'm running XP home and my graphics is an Nvidia 7300 gs with 512 RAM so it's similar to yours Bruno which is odd!
I mean I "can" use the shader tree but I have to purge memory constantly.

I've done a check and my background stuff is using roughly 500 Meg of RAM which leaves just 1.5 Gig for Vue, so if I put another Gig in, Vue should then have 2.5 Gig to play with, right! 
So would 2.5 Gig be enough to not have to purge all the time or is there still a reason why vue isn't freeing the memory, why can't they automate the purge memory thing!!!??

Injustice will be avenged.
Cofiwch Dryweryn.