The DC7700 was shipped with a recovery parttion NOT a "Restore Plus!" CD disk set. - are you sure the OS disk you have is for this machine?
Sounds like you've reimaged the drive so the recovery partition is probably long gone but was accessible by hitting F11 while booting.
You could order a replacment disk set from HP but you'll need to call
http://h10010.www1.hp.com/ewfrf/wc/document?lc=en&dlc=en&cc=us&docname=c00810334&printable=yes&product=3232027