Perhaps your best bet is cygwin, as mzilikazi suggested. It is used a the local college to provide Linux/unix type OS in an essentially windows environment. It work's quite well. I have it on my machine at work, a relatively button down envorinment, to give me access to GNU/Unix/Linux tools and compilers without having to reboot or invest in VMware.

I have Slackware on a partition on my machine, but the boot and reboot to get back to Windows require enough time to preclude quick excursions into a real O/S.