Import all users from 1 site to another

[HC.]

I have 2 forums and would like to import all users from 1 site to another any script for that?
Also would like to have a prefix added to the username of XX_username
any ideas how to do this?

[Opserty]

<a href="http://www.vbulletin.com/docs/html/impex" target="_blank"> ImpEx Import System</a>

For support ask on vBulletin.com impex forum. You can download it from vBulletin.com