data structure help needed

hi all, i am developing a site where users will be related in a parent-child type relationship. my users table is like this:

id     |     user    |    parent

---------------------------------

1      |    joe       |    null
2      |    bill       |    null
3      |   fred      |    1
4      |   john     |    3
5     |   frank     |   3

etc. Any user may have many children - what I want to do is traverse the tree in such a way that I can go up the family tree from any spot and see who is related. Anyone know of a good tutorial or a point in the right direction? I think this will require some recursive statement, which I have not done in PHP or MySQL before. Thanks Charles