The situation I had was that I had a portal already setup with a fairly minimal spec server running SQL for the back end and a seriously under-specced PC running web  etc.

The machine I have now became available so I decided to set that up and add it to the existing setup as a second web server before removing / decommissioning the PC. This would have meant that IIS and the default web site were initially situated on C: when the portal was added to that server.

To actually move the site to the E drive, I used a fairly caveman approach. I copied the inetpub directory to the E drive, went into IIS Manager on the server, selected the properties of the default web site and changed the home directory to the new location of e:\inetpub\... I then renamed inetpub on the C drive to something like oldinetpub to ensure it wasn't being used / needed.

I hope this provides a bit more background, let me know if there is anything else you need to know.