Seidai 正大 Software FairGame will convert the songs you bought on the iTunes Store to an unprotected format (using iTunes default encoder) and keep all the original metadata, lyrics and artwork.

It takes 2 min. 42 sec. to convert a 4 min. song to AAC on a MacBook Pro 2.16GHz

What you MUST DO (only once) to get FairGame to work:
 enable "Access for assistive devices" in the "Universal Access" system preference
 select "Place clip in Movie Timeline" in the "Import" preference of iMovie HD

Then you can simply:
 select some songs in iTunes
 click on the "Process songs" button
 then don't touch anything and wait until it's done...
(FairGame is scripting iMovie's interface to process the songs, don’t interfere)

Tested with: Mac OS X v10.4.8, iMovie HD v6.0.3, iTunes v7.0.1 FairGame free software to free you download