You are aware that PostgreSQL runs just fine on Windows?
But, to perform the conversion...
Study the pgDump and pgDumpAll utilities. They have options which will script the entire database (create a SQL script enabling you to run the script on another server and recreate the database structure and data)
After creating the script, you'll have to review it, line by line, in order to adjust the script for SQL Server's dialect. I recommend SQL in a Nutshell, Kline, Kline, and Hunt (2nd edition) by O'Reilly - it's offers a good command-by-command reference between several different SQL dialects.
And, you'll need to rewrite any stored procedures. plPg/SQL is similar enough to Oracle's PL/SQL that you could follow published guidelines for Oracle to SQL Server conversions.
"Lisa, in this house, we obey the laws of thermodynamics!" - Homer Simpson
"I have my standards. They may be low, but I have them!" - Bette Middler
"It's a book about a Spanish guy named Manual. You should read it." - Dilbert