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Are those users running software firewalls like zonealarm? If so, have them add your XOOPS powered site to the trusted sites list. Also, check your user info settings in your system admin -> preferences page, to make sure everything is set the way you want it to be.
As for the polls module, you can see it works fine here, so you'll have to be a bit more specific about what isn't working... Also, turn on php-debug (found in system admin -> prefernces -> general setings) to see if there are any real errors.
Herko