OWA picks up changes faster than outlook.

I'm trying to test the migration of users from our exchange2k server to exchange2k3 on a completely different domain which involves exporting the mailboxes, deleting the mailbox, creating a new mailbox and then setting it to forward mail as an external smtp recipient (on the other mail server on another site).
However any changes I make to AD are taking forever to appear in Outlook2000. The old username (with old address's) still appear in the address book and the new user doesn't appear for at least 1-2 hours after running the recipient update service)
However, if I use the OWA interface the user appears a lot quicker (about 5 minutes after running the recipient update service).
As I have a lot of users I don't really fancy waiting around for AD or something to realise the email details have changed.
Any ideas?
Update I think this is something to do with cached/non-cached mode. If I create a new profile in non cached mode the new user appears when I type in _arghhh and press ctrl-K in the TO field. However it doesn't appear if I do the same thing in the cached mode (and yes I have downloaded the address book (several times))
update2 I was close on the last update. I need to update the offline address lists by right clicking and choosing rebuild. Then a download in outlook of the address book and I can see the changes. Still no idea why it takes so long. I'll remove _argh now and see how long it takes before this disappears from the address books.