Dizkus

1) download your files in your provider directory. Name: XForum. You must have this directory
scheme: [NUKE]/modules/XForum/[XForum files]
2) Check that settings.php and jumper.php are Chmoded 666 or 766 (writable)
3) Login as admin in Your site and use this URL to start install:
http://[YOUR site here]/modules.php?op=modload&name=XForum&file=install
and follow instructions step by step.

i did all that but http://[YOUR site here]/modules.php?op=modload&name=XForum&file=install doenst work its a error page.

is it cuz i have 0.723 not .71-.72 ?

What error page? Are you getting a 404? that means the install.php file either

A) Doesnt exist
B) Isnt chmod at least 644

I've installed Xfourm on PN 0.723 quite a number of times and never had any problems. Make sure that settings.php and jumper.php are chmoded 666 or 766 (writable). And make sure the Xforum directory is in the modules directory and not the Modules directory. I had done that mistake once and took quite a lot of time to realise :P