So what I think you should do is:
in the first combo box you list all tables (don't know if you know how to do this).
On the after update event of the first combo you put this code:
dim sTable as string
dim sSQL as string
sTable = me.combo1
sSQL = "SELECT * FROM sTable"
me.combo2.RowSource = sSQL
'don't think you need the next line
this should give you the values in the second combo.
For the thirth one, you do kind of the same, but you change it where needed...
Is this enough, or do you need more?