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As you prolly know, the version numbers has changed, so the version you are saying is prolly XOOPS 1.2.2. If it is really that version you will have to update first to XOOPS 1.3.10, and then from that to XOOPS 2.0.6.
I'm not really sure that you can directly update from XOOPS 1.2.2 to XOOPS 1.3.10, since as far as I remember there where a lot of database changes from 1.2 to 1.3, and I don't think the upgrade is in the full package.
You might want to contact Herko to be able to see all files XOOPS has ever released to update on that way.