Yes I checked yesterday in the BIOS the SATA settings. I found something like:
Automatic RAID detection or ATA
This works fine for Redhat 4.0, but not for 3.0.
I discovered that Redhat 4.0 contains several different SATA drivers. I could select them when the installation doesn't find any installation medium, however without success. 3.0 doesn't have these drivers.
Now I have systems with SATA and Redhat 3.0 preinstalled by DELL working fine. Maybe it is worth to contact DELL about this ...