IM1.41 > vBulletin Conversion?

[richiebgood]

To cut a long story short I am splitting up my site due to some sections being bought. The half the site will be transferred to vbulletin on the same domain and the other half will be kept as IM1.41 on a another domain.

Question:
How hard is it to transfer Im1.41 to vbulletin - I am only interested in posts and members. There is IMPEX for converting phpbb2 to vb, but I do not how how it will handle the category hierarchy mod that is part of 1.41.

Things like the album, attachments, gallery will all be remaining on the IM site so if they survive the transfer, they will be deleted anyway. Signatures and avatars can be lost also, as members can reset these them selves. It's only the forums with commercial interests that are being imported.