Here's a XFCE Ambiance Style Theme I made for Windows 7.
[Note: This Theme will disable Windows Aero.]
Wallpaper is GNU from Xubuntu 9.10 Karmic Koala.
Download Here

Software You Need: 7-Zip, Pidgin, Web Browser, Windows 32 or 64-bit.

Edit Jan.19.2013: Link on step 4 is 404. Download a zip containing en_US.aff and en_US.dic Here.

1. Open CMD as Administrator.
2. In CMD, enter cd %ProgramFiles(x86)% if your on an 64-Bit OS or cd %ProgramFiles% if your on 32-Bit. Hit enter.
3. Type in: mkdir pidgin\spellcheck\share\enchant\myspell\ then hit enter.
4. Download and save the American English Dictionary to your Desktop.
5. Open the Dictionary's .oxt extension inside 7-Zip.
6. Open %ProgramFiles(x86)%\pidgin\spellcheck\share\enchant\myspell\ in Windows Explorer.
7. Extract en_US.aff and en_US.dic to the myspell folder.
8. Restart Pidgin.