Not quite sure what you're wanting kerr, a redirection script like cjb.net?
If so, check hotscripts.com, I used one a while ago, form memory I think it was called 'RedLounge'.
If you're planning to make your own, it's possible, I started making one a while back, you need to ensure though that you have a dedicated IP address for the website, this is required to catch all the wildcard subdomains (******.domain.com).
I have a script for that... if thats the kinda thing you want.
You can see it at www.6yd.net. Is that what you want? I can pass on that script to you for $30 if you want, although I'd obviouslly need to make it slightly more legible (coding-wise) as I'm a bit messy haha