Urgent help needed 3G 4.1(6.15.00)

Hi there. i have an iPhone 3G 4.1 (modem 6.15.00) and it was too much sluggish and battery sucking. i tried to downgrade it to 3.1.2 (from 4.1) but it's stuck in recovery mode by following all the steps of this: iClarified - iPhone - How to Jailbreak Your iPhone 3G on OS 3.1.2, 3.1.3 Using RedSn0w (Windows) please reply me soon as to what should i do?i was trying to downgrade it to lower software and from Google search i found that it can only be downgraded to 3.1.2,i wanted 2.2.1 anyhow....can anyone tell me to which firmware i should downgrade.