How do I run a large script with many inserts without running out of memory?
The maximum batch size for SQL Server 2005 is 65,536 * Network Packet Size (NPS), where NPS is usually 4KB. That works out to 256 MB. That would mean that your insert statements would average 5.8 KB each. That doesn't seem right, but maybe there are extraneous spaces or something unusual in there.

My first suggestion would be to put a "GO" statement after every INSERT statement. This will break your single batch of 45,000 INSERT statements into 45,000 separate batches. This should be easier to digest. Be careful, if one of those inserts fails you may have a hard time finding the culprit. You might want to protect yourself with a transaction. You can add those statements quickly if your editor has a good search-and-replace (that will let you search on and replace return characters  like \r\n) or a macro facility.

The second suggestion is to use a Wizard to import the data straight from Excel. The wizard builds a little SSIS package for you, behind the scenes, and then runs that. It won't have this problem.