There is an excellent blog article writen by Richard Seroter on how to enable static methods in the BizTalk 2006 rule engine. Seems that for the time being you have to get into the registry. I wonder why these essential functions are always hidden? Are there any caveats?

You can read it here

Let’s see if it will make it into the the final release. This would eliminate the need for all these simple .NET conversion functions that are needed currently with BizTalk 2004. No need to wrap it in an IFactCreator, and no need to create an instance to test the rules.