Migration assistant doesn't like me :(

If booting it up for the first time and using the MA, it's possible (though I have no idea off the top of my head) that it requires user information to be transferred over as well with apps and the like (because some apps contain data that is stored in the home library in order to function). My guess would be to create a new user first (which will create a new home directory), and then run the MA in order to transfer the other data. Or possibly, there is just too much data to be transfered. While you may have 120gb drive in it, formatting takes up about 10-15 gbs and the base install takes up at least 20gb's with all the printer drivers and language files and iLife stuff. You could go about and perform a fresh install on it and customize the installation to remove those unnecessary files.

Or, if I'm reading it wrong, transfer over the user data first, and then go about using the MA after the machine is running (accessed from the Utilities folder) to transfer everything else.

As far as I know, bootcamp can not be migrated as it requires a separate partition in order to work. Even if you had the other partition pre-made, Mac OS cannot write files (only read) to an NTFS formatted volume and wouldn't be able to do much anyway. In that case I would target disk the old machine to the new one with a firewire cable and attempt to manually transfer over any personal data from that bootcamp partition to your Mac HD, which can later be copied to a flash drive or burned to a disk in order to get it back to Windows.