Ah hah! Joel Spolsky posts a technique that allows Vista to instal on VMWare: edit the .vmx file (a plaintext file) and add the lines svga.maxWidth="640" and svga.maxHeight="480". This allows you to see the Vista install (with crappy posterized colors). After Vista boots, install VMWare Tools, remove the lines from your .vmx and Bob's your uncle. Just tried it and it works.
Update: Corrected link.