The lack of a working installer, however hasn't stopped enerprising geeks from finding a way to do it (and sharing it).
The first hack for getting PowerShell RTM to run on Vista RTM was a blog post I pointed to yesterday. Last night, superstar MCT Fermin Sanchez posted some updated instructions. I followed both sets of instructions and now have PowerShell 1.0 RTM running on Vista RTM.
...CUT...
Note: I am pretty certain this is not supported in any way, shape or form. But it takes about 10 minutes and seems to work well enough. Please do not do this on a production machine.