*TEASER*
For this tutorial, I'll assume that you have:
- MGMaps(the application)
- GPS hack
- MicroSD card
- *drum roll*A CELLPHONE- Either an Eternity or an >Impression<(my poison)
Note:
You MUST install MGMaps through TKFileExplorer or you will not have the permissions to access the folders necessaryStep 1Select the portion of the map to cache and specify the zoom levels on this site:
http://www.mapcacher.com/(Follow the instructions on the site) You should have a .map file upon completion.
Step 2Download gMapMaker here:
http://www.mgmaps.com/cache/gMapMaker-setup.exe (I swear on my gorgeous AMOLED screen that this isn't a virus(or nudie pics))
Step 3Open up gMapMaker.
Note the Cache folder because that is what you're going to be uploading onto your SD card.
Hit go and direct it to the .map file, created earlier.(Make sure that the operating mode is set to MGMaps mode-using the .map file)
My other settings were as follows: Max Parallel Downloads: 3, Hash size: 97
You can experiment depending on your preference.
Step 4After the maps finish downloading, which can take a while depending on how many levels you've chosen, copy the MGMapsCache folder over to your MicroSD card.(I'm assuming you know how)
Step 5On your phone, open up MGMaps, go to Settings>Map Browsing, check Stored Maps and Offline Mode, Scroll down to the Storage Path, select it, hit menu>browse>[direct it to the MGMapsCache folder-e.g. Mmc/MGMapsCache], hit menu again and save.
Step 6Close and reopen MGMaps. Once again, we open up settings>Map Types and check Google Maps.(the first option under Googe) You can also uncheck all of the other map types as you won't be needing them.
Step 7If you've unchecked all other map types, you should see the maps that you've cached, if not, press zero(multiple times, if needed) to switch the map type.
And that is it ladies and gents. 
I'm open to any questions.