The good folks from Bamboo Solutions (these guys make tons of webparts, check them out) have made a setup bootstrapper called WssVista for WSS 3.0 / MOSS 2007 SP1 that enables it to be installed on Windows Vista SP1. You can download it here.
Yes, you are reading well....SharePoint running on Vista. I still can't believe it...
The tool bypasses the built-in setup condition that prompts for a server operating system, thus enabling the SharePoint files to be unpacked to your client machine. Later, the familiar sequence of Setup, Configure SharePoint Tools and Technologies, Central Administration, IISRESET, rinse, repeat...
The IIS 7 that ships with Vista Service Pack 1 is virtually identical to the one that comes in Windows Server 2008, albeit with minor performance downgrades. Toss in the SQL Server 2005 installation on your Vista, and you have the environment for SharePoint "Developer" Edition, hacked provided by Bamboo Solutions.
Of course, it's TOTALLY UNSUPPORTED by Microsoft and it seems that it will be unsupported forever for a long time. So, install it only for testing purposes and not in a production environment.
**Bamboo Solutions Walkthrough for WssVista Tool
Microsoft semiofficial statement about SharePoint on Vista