Can I install Python windows packages into virtualenvs?

Yes, you can. All you need is

easy_install binary_installer_built_with_distutils.exe

Surprised? It looks like binary installers for Windows made with distutils combine .exe with .zip into one .exe file. Change extension to .zip to see it's a valid zip file. I discovered this after reading answers to my question Where can I download binary eggs with psycopg2 for Windows?

UPDATE

As noted by Tritium21 in his answer nowadays you should use pip instead of easy_install. Pip can't install binary packages created by distutils but it can install binary packages in the new wheel format. You can convert from old format to the new one using wheel package, which you have to install first.

I know this is quite an old question, and predates the tools I am about to talk about, but for the sake of Google, I think it is a good idea to mention it. easy_install is the black sheep of python packaging. No one wants to admit using it with the new hotness of pip around. Also, while playing registry tricks will work best for non-standard EXE installers (someone built the installer themselves instead of using distutils, and is checking the registry for the installation path), there is now a Better Way(c) for standard EXE installers.

pip install wheel
wheel convert INSTALLER.EXE
pip install NEW_FILE_CREATED_IN_LAST_STEP.whl

The wheel format, introduced recently as of this post, is the replacement for the egg format, filling much the same role. This format is also supported by pip (a tool already installed in your virtualenv).

if for some reason pip install WHEELFILE does not work, try wheel install WHEELFILE