First thing to do is to backup your Outlook PST *just in case*
http://www.hpcfactor.com/support/cesd/s/0078.asp
Contacts are easy to clear, just select all and delete them. Calendar though aren't.
On the host delete the ActiveSync profile for the deivce.
Reconnect it and get the partnership wizard up, specify that you only want to sync with the one computer then when you get to see the sync options, deselect all of then
(inbox, calendar, contacts, tasks etc
) . Finish the wizard.
Tools > Options Sync Mode > Manual
Rule > Always replace items on my device
Now just go back to Sync Options and select calendar
OK that and hit the sync button, with any luck items will be replaced on the device. Once you're sure the calendar is alright, the rest is fairly straightforward.