system
2
Hi,
I’m a little late for the answer 
But I’m hang a little further than you…
I made the same mistake as you and the only way I found going over it is to uninstall SQL Express 2005 (3 parts) and reinstall it.
There you can specify mixed mode authentication and you must specify a password for the SA account…
But now ADNM install still say me he “couldn’t locate SQL server XXX”… Perhaps because SA account is deactivated? Don’t know and still searching!
Regards,
Gerard.