So, without further ado...
Step 1: Materials
-Some way to connect the guitar into the computer
-A software application called "MIDI Guitar" (http://www.jamorigin.com/midi-guitar/)
-USB-to-MIDI Cable (Important that it's MIDI OUT)
-MIDI-Pro Adapter for Rock Band 3
Step 2: Steps
2. Connect your USB-to-MIDI cable
3. Start up MIDI Guitar and set the input to your device, and MIDI output to your MIDI cable
4. Connect your MIDI OUT to the MIDI-Pro Adapter, connecting that to the console
5. Viola, your finished!
Step 3: Work in Progress
Step 4: Oh, And, Uh...
GUITAR - Fender Starcaster
LINE IN - M-Audio MobilePre
MIDI CABLE - eMedia USB MIDI Cable
WORKING - In Progress
So send me what you used and if it works, I'd really appreciate it ^-^