There is an immediate issue and also a few possible other issues. 10GB is quite a large file. XitNotes is typically extremely fast at export - especially if Outlook and Notes are not running and logging is disabled.
XitNotes can export practically any size Lotus Notes mailbox but Outlook 2000 only supports mailboxes (PST file) up to 2GB in size. 10GB is way past that limit so it was probably generating errors continuously and also probably causing memory leaks in the error exception process which would also slow the export. Outlook 97 - 2002 does not warn that the size limit has been reached/breached. This is a common Outlook issue.
You can upgrade to Outlook 2003. It supports mailbox (PST file) of up to 33TB in theory. 10 GB however is still very large from a practical point of view. Outlook performance may suffer but should handle it.
The data can be broken into folders and those folders exported to individual PST files (New PST file for each batch). The Lotus Notes advanced option can be used to select folders.
Other possible issues
Is there enough space in the destination? A minimum of 10 GB free space is required for that mailbox. You may need more.
Is there are any custom views? They can cause data duplication in the export. You can use the Lotus Notes Advanced options to deselect these duplicate views. An example of a duplicate view is the "All Documents" view. This contains all information in other folders. By default XitNotes excludes it. If you or you administrator have created custom views XitNotes doesn't know so it will export by default.