I was under impression the partition was fully within <= 4GB area, not over it? Anyway, this is assuming he's using old scsi or ffs... Old scsi and ffs are fine as long as the partition is fully below 4GB limit.
Like Brian pointed out, that particular error message is due to bug in the installer, it handles disk size signed, not unsigned. Thus, if the partition has more than 2^31-1 bytes free, the installer will see it as negative number. This problem can be worked around by filling the disk until the (free_bytes & 0xffffffff) becomes <= 2^31-1.
