Not sure what's going on with minimenu. Mine detects it fine.
As for it not running from xfce, have a look in /tmp/pndrunpsx4all-1 or something along those lines. If you're still none the wiser, post the contents here.
The latest build from the beta testing thread works well for me.
But this problem sounds like what Fennec was doing for me until I realised that I must have had a broken download (the filesize was very different). Might be worth downloading it again if you haven't already.
In MiniMenu, PNDs do not autoappear unless you reboot or do a Rescan Applications.
Most of the time PNDs not appearing is due to unfinished downloads.
The PXML Data is at the very end of the PND-file - so if the end is missing, it won't show up anywhere.