Where do i get instalous and a bios pack??
I'm pretty sure the 3G doesn't have to be authenticated by apple for firmware updates/changes.
If it says it's failed after spending 5mins loading the firmware, you need to use recboot to bring it out of DFU mode..
I haven't done it for a while but it should be possible to go back and forth to any iOS on the 3G
Redmondpie is a pretty useful site.