Oh man, you didn't have to format! Well, for future reference its just a little registry editing that needs to be done. Warning, though, any programs installed AFTER the system disk became the G: drive may need reinstalling because it will be looking to the G: drive and not the C:. Anyhow, to change the system disk, do the following...
1. Run regedit and goto the following key:
2. Change your \DosDevices\C: listed in there to something like \DosDevices\X: (or anyother non existant drive).
3. Now change the \DosDevices\G: to say \DosDevices\C: (reason we changed the original to X: or whatnot is so there was no duplicate drive letter, get it
4. Finally all you have to do is change the \DosDevices\X: (or whatever you renamed the original to) to be \DosDevices\G: or whatever drive letter you want it to be and that is free to use.
Thats it, just exit the registry and restart (it wont show correctly until a restart).
Also, DO YOURSELF A FAVOR!!! Backup you registry before doing this and DONT touch anything else listed else you may have worse problems to deal with.