adding USB hard-disk

[n dhert]

I have an external USB hard disk, wich already has unix dirs and files on
it.
When plugging into a OpenSuse10.3, the dirs and files are immediatly
available under /media/disk-1 as unix dirs and files.

When plugging into a FreeBSD7.2 system:
on console I do get the messages:
umass0: <Prolific Technology Inc. ATAPI-6 Bridge Controller, class 0/0,rev.
2.00
/0.01, addr 2> on uhub4
da0 at umass-sim0 bus 0 target 0 lun 0
da0: <ST330083 1A 4.60> Fixed Direct Access SCSI-0 device
da0: 40.000MB/s transfers
da0: 286168MB (586072368 512 byte sectors: 255H 63S/T 36481C)

# camcontrol devlist
<ST330083 1A 4.60>                   at scbus0 target0 lun 0 (da0,pass0)

# ls -la /dev | grep da
crw-r-----   1 root  operator    0, 113 Nov 18 14:40 da0
crw-r-----   1 root  operator    0, 117 Nov 18 14:40 da0s1
crw-r-----   1 root  operator    0, 118 Nov 18 14:40 da0s2
crw-r-----   1 root  operator    0, 119 Nov 18 14:40 da0s3
but
# mount /dev/da0s1 /mnt
takes a while (drive spins), then
mount: /dev/da0s1 : Invalid argument
same result for all slices

Why is this and how to remedy?

(I can mount an USB memory stick with
 mount -t msdosfs -o -m=644,-M=755 /dev/da0s1 /mnt)