I have 10.5.8 running quite happily and connected to the router via wifi but I cannot see any of my other devices on the network, they are all running windows (XP and 7), I can't even see my iPad. I managed to connect a pc to the Dropbox and transfer files from pc to Mac. Everything I've read on the web says open network in finder and select the pc, the folder is empty!

Sorted.

on the pc running windwows 7 go to network and sharing/advanced sharing setings/homegroup connections and change from default 'allow windows to manage' to 'use user accounts'