Wow I obviously gave way too much info in the original posts as I am not after Exchange or Outlook help at all (unless someone has seen this exact fault and knows a better solution than Microsoft?).
But thanks for the feedback anyway. All posts are useful, even if just to point out I could have worded things much better (not enough sleep!).
I really just want to know how to get the BB up and running again easily after I restore the mailbox and if it will lose all his old emails off it in the process.
Outlook 2003 has a 20GB PST and OST size limit so that is not the problem.
I agree that the fix I am doing may not solve it but it is all Microsoft are giving me to go for at the moment so I have to try it. Hardware failure and badly configured virus scanner a while ago could have caused corruption so this may well work (by excluding the corrupted messages when restoring using Exmerge or Outlook PST).
Going to just do it tomorrow and from the post above I am sure I will stumble my way through re-enabling his BB (have warned the user that it might not be working staright away).
PS: I think I need to change the user name I use around the place as people always assume I am of the fairer sex