I installed PyQt5 globally on my win7 system (python 3.3), using the installer provided from the official riverbank website.
Then i created a new –no-site-package
Both "pip install sip" and "pip install PyQt5" inside the virtual enviroment are returning errors.
If the errors you're referring to are:
Could not find any downloads that satisfy the requirement [pyqt5|sip]
and
No distributions at all found for [pyqt5|sip]
Then this answer should shed light on this. Basically, PyPI is only providing a link to the homepage and/or source -- not a downloadable package or egg. Here are the links to PyQt5 and SIP PyPI pages. I know it seems strange that a package manager wouldn't provide packages, but that's the way it is.
You'll have to download, compile, and install sip and pyqt5 from source, inside your virtualenv. I wish I could provide details but I'm currently working through this myself.