my, that's a big hammer you have there...
Yes, the 'commit' does unlock the table. It tells the database server to 'make it so'. 'rollback' undoes whatever you did, provided you haven't already done a commit.
The lock ... select max... is really a brute force and ignorance (in the non-pejorative sense) approach. It will kill you on a multi-user transaction system. A data warehousing system can probably get away with it, but it is still poor form. Take a few minutes to implement the method Ben pointed to. You'll save yourself mysterious headaches later.
