WordPress MU

Is it possible to swap my install from subdirectories to subdomains after i already installed it?
Can I just tweak something in the control panel for this?
Or do I have to delete and retry?

Possible, yes.

PITA, kinda.

More time consuming than anything.
If you're just now installing, and haven't really tinkered around, it would be quicker to just reinstall it.

If you already have users, then there's a lot of edits to be made in the db.

Paths, addresses, global options and such... it can be quite overwhelming. And if you miss just one edit... oops!

I'd recommend making a duplicate of the site and the database, making the changes to the database and then testing. if it all works right you're done. While doing this test it'd also be a good idea to suspend new signups by replacing your signup page with a placeholder. Heck maybe even put in a email signup to get notified when signups are available again.

thanks guys, i think i'll just delete them, delete the db, and reinstall.
i don't have any users on it yet anyway.

And you have the virtual subdomains set up in Apache, right?