Same issue here. For some reason the Dell Bios won't recognize the drive as a 5.25, and only allows 3.5 as an option. Once I get into XP, its still listed as a 3.25, and won't read 5.25 disks. Very disappointing, I've looked around quite a bit and unfortunately I think its a bios limitation that can't be resolved unless anyone has any magic answers.
PS SpeedStep has the correct hardware connection information listed. Unfortunately unless someone else knows something magical, its not a hardware connection issue, its a bios limitation.