You did not give us your version of Openserver - the Perc3 may not work on versions prior to 5.0.6.
From my notes on the last 2 Dell server installs I did:
Adaptec Based PERC
(Mentions Adaptec on POST messages)
IDE CDROM: type defbootstr link=percraid
SCSI CDROM: type defbootstr link=percraid Srom=alad(0,5,0)
LSI or AMI Based PERC
(Mentions LSI or American Megatrends on POST)
IDE CDROM: type defbootstr link=amird
SCSI CDROM: type defbootstr link=amird Srom=alad(0,5,0).