Page file is virtual memory that is actually on the hard drive to make more RAM appear visible to Windows. It should be 1.5x the physical RAM. If you're just using it for the video camera monitoring I would assume that you can get away with a 512 MB (or maybe even 384) RAM install of Windows on a 4 GB partition and be fine. You can maybe go a little smaller, but I wouldn't risk it as service packs and the like require the additional disk space to install.