I've seen that vista eats up a lott of RAM even in idle instance.

I dont think the graphics quality which vista give does not justify the RAM usage.

If you want to see a video of Windows Vista and Beryl desktop environment in Linux, Here are few links

http://youtube.com/watch?v=xC5uEe5OzNQ

http://youtube.com/watch?v=2eDI4-IH58s

Beryl uses very less amount of RAM while its running.