Oficially you can run up to Tiger on it. I don't know if Windows Seven will work, but you may install Windows under a program called QEMU. You may also try using Virtual PC.
It's strange. Try cleaning your system cache(delete all content from /library/caches and /users/YOURUSER/library/caches), repairing disk permissions and reseting the PRAM(press Command+Option+R+P before your Mac start up).