Anna,
I will assume you have a hard drive with multiple partitions, or multiple hard drives, one of which is labelled C:, other is D:... and the D: is NOT shared on the network.
If you use Office 2000's defaults for offline storage, the current path is probably similar to mine:
In Windows 2000:
C:\Documents and Settings\"user name.domain"\Local Settings\Application Data\Microsoft\Outlook
Before switching any settings, quit Outlook.
You set this outside of Outlook by right-clicking on the Outlook icon on your desktop (or select START >> Settings >> Control Panels >> Mail). Next, select the profile your user defaults to (default name is Microsoft Exchange Server) and double-click it or select "Properties".
Next, click on the "Advanced" tab, and click on the "Offline Folder File Settings..." button. In the "File" field you'll see the full path name for the current Offline Folder file. It's probably greyed out, meaning it's locked.
Make sure the system is at least temporarily set to allow viewing of hidden AND system files. Follow that path until you find the OST file. You'll move it later...
Now, click the "Disable Offline Use" button. This unlocks the settings so they can be changed.
Move the old .OST file to the new location you wish to use (we use a folder on the drive labelled "Mailbox_username"

. Now all you need to do is re-enable offline settings and point to that old .OST file... Click the "Offline Folder File Settings..." button again, and BROWSE to the new location of the .OST file, select it, and accept it. Poof, you're done! Turn folder view settings back to hiding system files and restart Outlook. Make sure they do this while still on the network, as it may take a bit to resync the OST file over a modem connection.
Hope this rather lengthy message helps!
Dan