Yes and no. Generally, with that amount of RAM you can disable it and shouldn't have any significant problems. If there would be RAM shortage - the operating system would kill a process. There is no way to prevent that so it can be dangerous for systems with too few RAM. But you shouldn't run out of RAM with 4GB in normal circumstances.
The virtual memory system will continue to work, but without disk-based swap to
'cover' that virtual memory. I have to admit i'm not sure how windows handles this. Tom did feature an article about this i remember.