Hi Tom,
We developed something similar to it:
- redirect to website/page according to IP address
- redirect upon login
For the first feature we developed a module to manage those redirects.
For the second feature we developed a simple module that managed custom fields for websites, and related the groups. Then we subscribed to the onExtranetLogin notifier, and if the user belonged to a mapped group, he would be redirected to that website's first page.
Nuno