Thankfully there is a command-line Sql server client Microsoft thoughtfully provides together with Sql server. If you're not able to import a large sql file using SSMS, navigate to the Binn folder of your Sql server folder (C:\Program Files\Microsoft SQL Server\100\Tools\Binn here) in Command Prompt, and type the following:
osql -S databaseserver -U username -P password -d DemoDatabase -i c:\demo.sql
That executes the file C:\demo.sql on databaseserver in the context of DemoDatabase using the login data provided. This will scroll a bunch of query results in your command prompt window. If you'd rather examine these results in detail later, the -o parameter writes this info to an output file:
osql -S databaseserver -U username -P password -d DemoDatabase -i c:\demo.sql -o c:\output.txt
That should work, even when SSMS chokes on the sheer size of your query file.