Trouble setting up python on Powershell on Windows Vista

While setting up python according to the tutorial (typing "python ~\Desktop\ez_setup.py" in powershell), this error came up:

c:\python27\python.exe: can't open file '~\Desktop\ez_setup.py': [Errno 2] No such file or directory

but when I typed in "python ~\Desktop\" and pressed the tab button, it fills out the absolute path and the command worked.

I'm not sure why the tilde doesn't work, and not sure if this is a Windows, powershell, or python problem.