SQL Server is not really any better than MySQL other than its current support for triggers and stored procs. We use bothin production evironments and SS is definitely lacking things, like no regex in sql can't manipulate text fields in line and others.
And since MySQL will have both soon....
anyway back to your question...Use the MSSQL functions. You should for the most part be able to do a search and replace to convert the function calls.. Also don't forget to uncomment the MSSQL server dll in the php.ini file to make it available.