WP3 Converting to Subdirectory While Preserving Links

Hi,

I tried searching the forums for an exact solution for this but I haven’t found one that matches this situation. Sorry in advance if the solution is covered but I’ve missed it.

Question:
Is there a relatively painless way to convert an existing WP implementation (installed directly in root Public directory) to a subdirectory format without losing link integrity (permalinks)?

Background:
The reason I’m asking is that I’d like to setup a WP Network using WP3 but it tells me that I can only use subdomain format due to my current installation. I only want to set up network via subdirectory format. But in converting to subdirectory I’m afraid of losing link integrity. The other reason I’d like to do this is that I have two unique domains that I’d like to use for the network (multi-domain setup).

If anyone can please advise how to do this (via plugin or manually) it would be much appreciated. Thanks!