I would even go so far as to suggest you create each company site as a child 1st. www.bigcompany.com, www.bigcomapny.com/little1, www.bigcompany.com/little2 etc. Then once the child is created add the alias for the "real" domain name and make the required changes in IIS.

So in IIS you would set up another website pointing to the child portal directory?  Is this in the docs somewhere?

I even go so far as to create the children with folders that identify the portal. Makes it much easier when managing files on the server or via ftp.

How do you do this without buggering the whole thing up since DNN creates the child portal directories automatically?

Thanks so much for your advice and suggestions.

I'm almost there! Thanks for your tutoring! 

So when I setup DNS for each site, they would all point to the same ip address.  Then I would add entries for each URL in the siteURLs.config file.  Sound right?

I think I am going to go with the one portal plan.  I have a good back-up procedure so I can recover pretty quickly from an update gone awry.  In my case, one of DNN's big appeals is the ability to add functionality (modules) to all sites at one time.  

Thanks for helping me out on the decision.  Thanks to Larry too.  Although I'm not using your strategy, It was a great help to have a heads up on what to consider.

Perfect!  Thanks again for all the help.  Now if I can get web farm support running properly I'll be off to the races.

LD