sorry for the old post, but I did try it and it refuses to activate swap on a non-swap enabled device. Now I assume that you had done that a while back (judging from the hda device) so there are probably now some extra safety checks (good thing too!) :-D well I'm sorry for your loss long ago :-)

[root@localhost ~]# swapon /dev/sdb

swapon: /dev/sdb: read swap header failed: Invalid argument

*edited the formating