Without changing anything in the core DNN code, an easy (free) solution would be to simply auto-forward users from the default HOME page to whatever page you want that user to go to based on their assigned security role(s).  That is, all users would still initially go to the default home page but would be immediately forwarded to their "personalized" page if they were a member of a specified role.

You could -almost- do this with the latest Text/HTML module via tokens and a small bit of javascript.  Unfortunately, user role info (token is [User:Roles]) is locked down and not accessible via the token replace feature.

An alternative is to use a "SQL" module to query the DB for the appropriate info and generate the needed javascript to load the appropriate target page.  I use such "SQL" modules all the time to add custom functionality without altering DNN or writing custom modules.
 
 
EXAMPLE:
Here's a simple, two-step no-frills example using the free AdvancedDataGrid module from Efficion Consulting (includes free source code!).  In this simple example, the ADG module will forward you to Google if the account's DISPLAYNAME is set to "mytest1", to YaHoo if set to "mytest2" or give an alert message for any other DISPLAYNAME value.

(1) Add the AdvancedDataGrid (ADG) module to a test page.  (Try this on a test page before using on your portal's home page!)
 
  If you're not familiar with the free AdvancedDataGrid module, I've blogged about it here (includes other enhancement examples/code):
 
    Part 1:  http://www.eguanasolutions.com/DNN_Blog/EntryID/2.aspx
    Part 2:  http://www.eguanasolutions.com/DNN_Blog/EntryID/5.aspx
    Part 3:  http://www.eguanasolutions.com/DNN_Blog/EntryID/13.aspx

 
(2) Go into the ADG module's settings and add the following as your SQL :
 
  select
    case DisplayName
    when 'mytest1' then
      '<script>window.location="http://google.com";</script>'
    when 'mytest2' then
      '<script>window.location="http://yahoo.com";</script>'
    else '<script> No match found.");</script>'
    end
  from users where Userid = [dnn:UserID]
 
Try It Out:
Create a test account and set the account's DISPLAYNAME to "mytest1".  Log in with the test account, go to the test page and you'll be forwarded to Google.  Go back to your site, change the account's DISPLAYNAME to "mytest2", go to the test page and you'll end up at YaHoo.  Neat!

 
For your scenario, you'll need to come up with a SQL query to determine what user roles get forwarded to what target pages on your site.  That query will be a bit more complex than the simple example I've presented.
 

I think you've presented a good question...I'll update this thread if I get some time to play with writing a query to match your specific need.
 
Cheers!
-mamlin