i've used a few different techniques. M2Crypto with a paypal integration, and the libraries on google app engine.
i'm pretty sure i had to build m2crypto, but no matter what it's not about installing the package into web2py, it's about installing it for your python install - web2py just imports from the libraries available to the python instance. i don't use windows, so unfortunately i don't have the gory details about how to get that up and running...
