There's some stuff here that should help, about half-way through.
http://www.simple-talk.com/2005/04/25/getting-started-with-setup-projects/
Basically you'll be doing a search for a registry key and using it to create
a custom folder.
You might discover that you can go to the User Interface view and simply
delete the Installation Folder dialog, but that's also the dialog that sets
the Just me/Everyone choice (per-user or per-system) and if you elimate that
choice, you'll get a per-user install by default, and that's perhaps not
what you want, so it's still Orca time.

Signature
Phil Wilson [MVP Windows Installer]
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>I am writing a setup using a VS setup project, but I want to eliminate
> the destination dir panel and just prereq that the homedir is already
[quoted text clipped - 4 lines]
>
> owen