Jeff,
You didn't say what version you're using, but check the FAQ's here: http://qa.sqlservercentral.com/faq/viewfaqanswer.asp?categoryid=2&faqid=154
There are two links from there to Microsoft's site depending on whether you're using SQL Server 7 or 2000. I've used the procedure on Microsoft's site for 7 with success several times. 12 Gig's sounds pretty large for a TL file. How often are you dumping the log? Hope this helps.
My hovercraft is full of eels.