Page rank is directly related to the number of backlinks you have. Just as kingofsanda stated, you should read through the google forum section for a better idea of how page rank works.
i know how the pr works anyway before http://www.interfans.org/forum was pr 3 as well as http://www.interfans.org/ now http://www.interfans.org/ is 3 and http://www.interfans.org/forum 0
http://www.interfans.org/ - 159 backlinks http://www.interfans.org/forum - 29 backlinks I would not worry about it for a few more months. Google does not update PR but 3 or 4 times a year. But the forums should have higher then a 0 with 29 backlinks. My sons forum had around 20 - 30 backlinks and stayed PR 0 for 6 months.