Aside from moving your site to a unix (doesn't have to be Linix, any box that runs PHP and MySQL will do, personally I prefer FreeBSD) server, you could either port GL to MSSQL / ASP (ugh); port GL to MSSQL and leave the code in PHP (better), or just add PHP and MySQL to your hosting service's plan.
Porting even the database is going to take some time, as there are non portable SQL statements littered throughout GL code (as well as most of the open source content management / weblog systems out there).
If you wanted to make a MSSQL capable port (I started down this road in GL1.5rc? a long time ago and gave up) you'd have to go through each SQL statement and remove the database dependencies from them. As I recall the big two that exist frequently in the code are the "LIMIT" keyword (MSSQL uses TOP) and "UNIXDATE(date) as ...". There are probably some others.
If you want to get something going quickly and inexpensively, a web host account from a Linux/*nix/*bsd provider offering PHP and MySQL can be had so inexpensively these days, just point your users to the site when required.
Or switch hosts altogether!