Updating T-Mobile G1 from 1.0 to 1.6

I have a T-Mobile G1 phone (Dev Phone) with android 1.0. To be able to install some apps, I needed to update it to 1.6. So I downloaded an update file and put it on its sdcard. But the update failed and now the problem is that I cannot boot the phone completely. First it asks for a SIM card. Although, I don't have a T-Mobile SIM card now, I could pass that stage with an AT&T SIM card. Now it wants me to login to my gmail account to boot up. But I cannot connect to Internet at the moment. There is no option for wireless too. When I press menu button it just shows me the settings for APNs. I believe in the newer versions of android, one can skip logging in to Google. But now I cannot even "adb shell" to copy other update files to the SD card. Any helps would be appreciated. Thanks,