[gardobus]

The MD5 mismatch isn't supposed to happen. That means that your download was corrupt or when you extracted/copied files they became corrupt. The MD5 check is just making sure that was you are about to install is exactly what the person who built the nandroid wanted it to be, with no errors or modifications.

Try downloading the Froyo zip again and extracting it again. Delete the folder you created in /clockworkmod/backup/ that had the bad MD5.

As for overclocking, I have had mine at 1ghz since they figured out how to overclock these things lol and I've had no issues. My brother and friends all have theirs at 1ghz also. Also, when you OC you can set it to slow down when the battery gets hot so it will never go over whatever temperature you set. You can also make it run SLOWER while asleep, this makes it run cooler when its just sitting in your pocket.