Free Music Software for Windows, from Shareware Music Machine. A nice list, though freeware software is notoriously hit or miss.

Harmony Central's audio editing software list for Windows has more detailed information on free, shareware and commercial audio software.

Musicware reviews music software, and maintains lists of free software. (Some annoying ads, but good content.)

Despite the availability of free options, I'm still tempted to endulge in Cakewalk products, at least maybe at the academic prices. But I fully intend to take the free versions to their fullest extent before paying hundreds, even if professional packages are the equivalent of Adobe Photoshop for audio.

Check out Cakewalk's Desktop Music Handbook, with lots of great background information on MIDI and digital audio.