After going through quit a bit of trial and error, I finally got the Maxima plugin for TeXmacs working on Windows, and I did not even have to edit any of the scheme files.
The linked file has the steps I used that worked on both a Windows 7 and a Windows 8 machine. Please feel free to forward the link to anyone in need of it.
If you find any problems let me know. I plan to keep this file updated when new versions of Maxima and TeXmacs come out.