I am installing DNN with an ISP, and am waiting for teh domain to be moved.  The way to access the site at the moment is xx.xx.xx.xx/$sitepreview/mydomain.org

when I try this I get  either

the site redirecting to mydomain.org/install/(cannot remember which page).aspx

or:

object reference not set

Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

Source Error:

An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below. 

Stack Trace:
[NullReferenceException: Object reference not set to an instance of an object.]
   DotNetNuke.HttpModules.UrlRewriteModule.RewriteUrl(HttpApplication app) +369
   DotNetNuke.HttpModules.UrlRewriteModule.OnBeginRequest(Object s, EventArgs e) +731
   System.Web.SyncEventExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +92
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +64

Can I turn the URL rewriting off (do I just remove various references in web.config?)  Or will this cause more problems further down the line - I was wanting to get thigs set up for the client, so we weren't held up by the URL transfer.

Thanks

Chris