SBUU takes SEVERAL minutes to load. If it hasn't booted in 10 minutes or so, then try downloading and reburning the DVD. What is your server's BIOS version?
Boot to the BIOS Setup (F2) and make sure that OS Install Mode is turned OFF - this setting is not required and limits the system to 256MB of RAM.
What RAID controller are you using in your 1800? Does your 2003 CD have SP2 on it?