Ah, hmmm, updated versions (as requested) are now available.I forgot I had to do that myself after porting. Anyway, these 2 scripts will do what needs to be done. I didn't have a copy of IPB 2 to test on, so you might need to toy with one of these two.

IPB 1.1.x to XOOPS 2.5.2
http://www.felocity.org/files/xoops_2.0.5.x/ipb1.1.x-users-to-xoops2.5.2.zip

IPB 1.3 to XOOPS 2.5.2
http://www.felocity.org/files/xoops_2.0.5.x/ipb1.3-users-to-xoops2.5.2.zip

Let me know if you have any issues with them! Good luck!
(now that these are finished I will probably also drop them into the downloads section)

Hi Jakobo, thanks for your update.
i get a warning after each user transfered to xoops
-Warning: mysql_fetch_array(): supplied argument is not a valid MySQL result resource in /home/luso/public_html/ipb1.3-users-to-xoops2.5.2.php on line 174
And the table xoops_groups_users_link is not updated.
IPB1.3 and XOOPS 2.5.2.

fixed. same file location, just regrab it. forgot to tack a '"' on the end of the select statement I was using (when adding the register users into group X feature).

Let me know if anything else crops up.