You are right to suspect something is up.
I usually take the average read speed, say, 60MB/s and with a 320GB, it should take about an hour and a half to do one pass.
Is this a SATA or PATA drive? SATA drive shouldn't have any problems regarding configuration parameters, but if youre using PATA, the drive could be using some slower mode like PIO etc. to access the disk, hence it's taking longer.