I had a look at an installation on a WinXP machine and got it working by adding the following keys to the registry:
Windows Registry Editor Version 5.00
[HKEY_CURRENT_USER\Software\Microsoft\DevStudio\6.0\Format]
[HKEY_CURRENT_USER\Software\Microsoft\DevStudio\6.0\Format\Output Window]
"FontFace"="Consolas"
"FontSize"=dword:0000000c
[HKEY_CURRENT_USER\Software\Microsoft\DevStudio\6.0\Format\Source Window]
"FontFace"="Consolas"
"FontSize"=dword:0000000c
The above lines set the Source and Output window's font to Consolas with a size of 12 points. It's an export by regedit so you can put it into a .reg file and import by opening that file in Explorer.
This solution from stackoverflow