I will add that I would start with free MIDI files. Yes some a crap but many are very good. Plus the drum tracks in the free files maybe identical or very close to the purchased files. I have used the drum tracks from the free MIDI files.
Thanks for saying this! I was going to mention that as well and spaced it. There are a number of decent free midi sources.
If your method was just a learning technique then just ignore this message.
BIG +1!!! Lining up the drums to the correct line can get annoying.