If myspace is not allowed at your school, you could get into a lot of trouble for using it... However, I'm here to help, not lecture:
The simplest method is a proxy website like vtunnel or similar. Many of these sites are blocked my the school as well, just search for a "myspace proxy" some time at home.
The next, which is slightly better, would be to use a random proxy and Firefox with the Foxyproxy extension. Search for a "proxy port 8080" for the best results.
The next easiest solution is GoPC (http://www.gopc.net/
). It appears to involve installing software and can be slow. I think they have an Internet-only version as well. This is rather unlikely to be block.
My final solution is setting up your own VNC server at home. Then access this with a VNC viewer at school. This is almost exactly like the above solution, but it runs off of your own computer instead of a server somewhere else. This is least likely to be blocked, but the most complicated.