Stuart,
I used the Benchmarking Wizard to validate my Production Server Enterprise Edition.
I had issues using the instalhostsl.vbs Script.
What I did is
1.Installed the Benchmarking Wizard
2.Created all 3 Host manually.
3. Imported the MSI in BizTalk Admin Console and installed the MSI in GAC.
But it worked perfect at first shot and gave good results.