In windows, you should have about 1x to 2x the memory of your computer (512MB) available on the file system for virtual memory. You can have more but the downside is that the system can enter a loop where it is constantly swapping memory out and in again.
Under linux the swapfile(adds to virtual memory) is afaik always it's own file system, so there should be enough even if normal file system space runs out, at least if you got it configured at all.
That being said, my memory problems with PS usually crop up later, not when I log in.