Pretty much got everything working now I think.
Disabled frontpage extensions because I don't think tehy're used, and was worried that they were a security risk.
Not sure how Sad handled redirecting from the old root of the site (www.sadgeezer.com/ [1]) to the new postnuke powered site (www.sadgeezer.com/html/ [2]) but I've put something in place that seems at least functional for now.
Currently running something of a hybrid version of postnuke.. I think we were running something like 0.7.2.3 but the replacement files I uploaded came from the latest build 0.7.5 and I had to upload the header.php file from 0.7.2.6 (the only other copy I had lying around) as the newest version seems incompatible with our themes.
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Links:
[1] http://www.sadgeezer.com/
[2] http://www.sadgeezer.com/html/