For those of you moving over to Vista maybe be wondering why your memory usage being reported in Task Manager is so radically different than it was in XP.

Well apparently it is because of the way that Vista utilizes that available memory. Jeff Atwood; over on the Coding Horror blog provides a nice and easy explanation of what is going on:

Those figures explain why I only have 6 megabytes of “free” memory in Windows Vista. Vista is trying its darndest to pre-emptively populate every byte of system memory with what it thinks I might need next. It’s running a low-priority background task that harvests previously accessed data from the disk and plops it into unused system memory. They even have a fancy marketing name for it– SuperFetch

You can here the full article here