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.