Don't let Altiris configure the computer to be part of the domain? Deploy the computer as a workgroup machine, deploy additional software and then run a vbscript to join the machine to the domain. After that you can replace the login backdrop and reboot.
If you're a Novell institution, leave the Novell Client installation as the last job, change the backdrop and reboot.
Although the keyboard isn't locked, your users will definently not be able to login... ??
Kind Regards,
Ian./