I\'m using virtualenv-1.4.5 on Mac OS X 10.6.2 (Xcode is installed) and Python 2.6. Here\'s what I get when I attempt to run a virtualenv...
Mac-Pro:pylonsd
There's also a bug with virtualenv on 10.6 See the ticket on virtualenv's bitbucket. Even if you solve the problem you're having you'll still run into another problem (I think image not found for Python.framework, but I don't remember - I didn't take any notes when I ran into this)
I did some investigating into this and I hope the root of the problem with be resolved with Python 2.7 - certainly people know about it, and submitted a patch to CPython to fix it.
However, it does seem like some people have had good results with 10.6.2 and virtualenv 1.4.5... or not using the system Python anymore (macports, build-by-hand).