I have an old 2g iPhone and I am jail breaking it now. Here is everything you will need except the actual 2.0 update to unlock. The date of this file is July 2, 2008 and it contains bootloaders 3.9 and 4.6, pwned 2.0 Pwnage 2.0.1, and instructions for an old 2g phone already upgraded to 2.0 via official iTunes update. (Be aware, these are not my unlock instructions. I got these from the comments on the dev team blog, just including them for convenience.)

I did not need to unlock I only wanted to jailbreak. To do this all I did was download pwned 2.0.1, Mac Only! I ran pwned and selected Simple Mode and iPhone. After it built the custom update I then restored in iTunes with the package created by pwned. Basically just follow the instructions and you are good to go ;) Now I simply restored my iPhone from backup to get my mail, contacts, and music back. YAY!!!!

If you have trouble or need help go to the official Devteam blog for guidence.

I did not include the 2.0 update. You can download in iTunes, after which can be found in /Library/iTunes/iPhone Software Updates. I would also go ahead a create a directory in /Library/iTunes named Device Support if it's not there.

This is the original Pwnage 2.0 tool DO NOT USE WITH THE OFFICIAL 2.0.1 APPLE UPDATE UNLESS THE TOOL GETS UPDATED. The Pwnage tool should get an update when you first run it and then you will be good to go. 

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Here is my freshly jailbroke iPhone 2G! Just sit back and wait for the installer...

and now INSTALLER 4, woot!!!