. Or maybe there's just the one (I thought there was a web-based version that had a network stack but I can't seem to find it). At least that way there wouldn't be any software to install and memory would be much less of a worry.
Back in...well I guess it was 2008...that was before I had switched to x64 windows so I couldn't use more than ~3.5 gigs if I wanted to...I would run OSes on that little memory all the time in virtualbox no problem. So if you did want to try virtualbox+minimal linux I think it is possible. My personal method would be to install the OS with a gig (or a generous amount anyway) of memory to the VM then reduce it to 512M for actual use. Maybe not be able to use anything else while it's installing but it shouldn't take very long.
Then you can setup virtualbox so you can SSH into the VM (SSH to localhost, if that makes sense). Advantage is if you're using an SSH client like PuTTY you can copy/paste stuff into and out of the term window. Great for taking notes and troubleshooting/saving some typing. My opinion best way to interface with the CLI while learning (again for note taking etc).