The Laptop should be able to run these virtual machines, although that depends a lot on what you're planning on using. You have two options, you use Microsoft Virtual PC, or you use VMWare. VMWare would be a better choice, so if you can get your hands on it on your school/college that would be nice (VMWare isn't freeware, Virtual PC is).
Furthermore I don't see any problems with having 3 OSes on your Hard Disk Drive with only 1 Partition, as long 2 are Virtual. I would like to note you the Virtual Machines are going to use their own space, as in their own Virtual Hard Disk Drive, so the files you install will be written into one big Virtual Disk file. Also a Virtual Environment will be going a lot slower (in some cases). I'd say, try it out.
Learn more about Virtual Machines here
If you have any more questions, or if I was a little unclear at some points, I'd be happy to help you again.