Can I install a post Nuke module in Xoops?

No. PostNuke and XOOPS are very different and although XOOPS is essentially based on PostNuke, this is a long time ago and both systems have evolved very far since then.

However there are some conversion scripts that have been released ...

please this this FORUM POST HERE

This Q&A was found on XOOPS Web Application System : https://xoops.org/modules/smartfaq/faq.php?faqid=107