I was able to update firmware 2.0.1 successfully to my first gen iPhone using PWNAGE 2.0.2.
The instructions below are for those who's PWN'd their iPhone prior. In my case, I PWNed the my first generation iPhone with 2.0 firmware.
1. Download the iPhone 2.0.1 restore firmware: here for 3G and here for 2G/EDGE version
2. Launch PWNAGE 2.0.2, choose your appropriate iPhone
3. Next screen, the PWNAGE will ask if you have a real iPhone contract (answer accordingly, this determines if your phone needs to be unlocked)
4. Provide your admin password when prompted and a custom firmware should begin to build
5. One more question should pop up again: If you have PWN'd before. (answer accordingly, if unsure, just say no)
If you never PWNed before, you'll need to following the screen prompt to get your iPhone into DFU mode. Much of what I learned is from this site when PWNAGE 2.0 first came out.
As for me, since it's been PWNed before, I simply launched iTunes and hold "ALT-Option" and clicked Restore; then I pointed to the newly build custom restore for 2.0.1 to complete the process.
I don't know how 3G iPhones would work, so good luck and please understand that if you decide to do this, you are doing so at your own risk.