We have several websites based around our www.thomasinternational .net domain i.e. /1 is our US site and /4 is our Uk site. When i search google for our website from our office in the Uk i get the US website is this something that i can change in DNN or is this more to do with google rankings ???

Google ultimately chooses which site it wants to rank for a given location of searcher and server and search phrase.

If you want your UK site to rank better (I assume it has a .co.uk domain?) then you will need to optimise that site more for the UK. Making sure it has a .co.uk domain will help. You may also want to try and get links from UK based sites. Perhaps the problem is that your US site has a lot of incoming links, and your UK site doesn't have many at all.

Google will tell you to locate the server in the UK but this isn't much use when you're leveraging a DNN installation to serve up the two separate portals.

My suggestion would be to analyse why your UK site isn't ranking well (for the moment ignoring your US site) and work from there. There could be a problem like a crawling error or duplicate content issues. Verify that it is OK first, and then start working forwards.