just upgraded from 2k3 to 2k7 and moved 2 mailboxes over to test with, got everything sending and recieving etc, however, after i moved the rest of the mailboxes over, i go to change the server name in outlook, and i type in the exchange server FQDN and then hit check name, it then resolves back to the old 2k3 exchange server? What am i doing wrong. But the 2 that i intially moved worked and continue to work fine

Did you by any chance use ADUC to move the mailboxes? There are known issues in using ADUC to administer exchange 2007 - in fact its not supported at all, regardless of the options / tabs you find in it.