Did you by any chance edit the register page with Frontpage or change anything else in that page ?
Either way, there is this code:
<head>
<meta http-equiv="Refresh" content="2; URL=http://www.whiplash.pp.se/forum/">
</head>
that causes this and somehow got moved outside the correct if..then..else statement.
Try uploading a fresh copy of register.asp, that should fix it.
Pierre