Error Downgrading to iPhone OS 1.1.5

[Fodd1337]

Okay, so, I have an iPT3 and have it running beautifully on 4.0, so my friend and I (who still have iPT1s) want to downgrade our first gens to 1.1.5 for the lols and awesomeness. I got the 1.1.5 firmware off of MMi's download page (thanks for the convenience) but now when I tried to restore, I got error 1600. Google search revealed I should go into DFU. Tried, same error. Tried over and over repeatedly going into DFU about 10 times. Now, I turn to you... I read somewhere that I might have to downgrade my iTunes to the most recent 7 build, is there any way I can have 2 iTunes' on one computer (7.x.x and 8.2)? Thanks for any help.

Bump? I need this help rather quickly, I'm going on vacation Friday