FIX FOUND! For those with the same issue, the fix involves using REGEDIT which is
very dangerous to your computer if used improperly. Tread carefully!
For some reason the installer was trying to use a temp directory that was incorrectly stated. The registry entry was looking for "Z:\PG\\MWOUpdate", and was causing an exception when the installer looked for it. I created a 'PG' folder on the root of my SSD dedicated for games. "Z:\PG\" is what I typed in the installer, and for whatever reason things didn't go very smoothly after that.
Simply using REGEDIT to change the key from "Z:\PG\\MWOUpdate" to "Z:\PG\MechWarrior Online\MWOUpdate\" allowed the launcher to run.
The key in question is located here, and it is named TEMPFOLDER:
HKEY_CURRENT_USER->Software->Piranha Games->MechWarrior Online->Production
Hopefully PG has all the info it needs to patch the installer (or launcher, whatever got confused) to correctly generate this registry key.
=====Windows 7 Step-by-step version=====
1. Run REGEDIT from the start menu's box by typing REGEDIT, then right clicking it, and RUN AS ADMIN
2. Navigate through the folders on the right-hand pane as above by clicking the "►" sign beside them
3. HKEY_CURRENT_USER, hit the ►
4. Software, hit the ►
5. Piranha Games, hit the ►
6. MechWarrior Online, hit the ►
7. Production, LEFT CLICK this folder.
8. On the right pane now you should see a list that appear to be files.
9. Right-click the registry key ("file") called TEMPFOLDER, and click MODIFY
10. Ensure that the directory is pointing to your "MWOUpdate" folder with no double "//" anywhere in the line.
11. Re-start the installer from scratch.
Edited by The Justicar, 24 September 2013 - 12:18 AM.