Hi, what have you tried? some links to what Ubuntu articles you have read may help us help you.
Can't you just install it with the software manager?
I use kde4 and openbox, and with kde4 I have Dolphin and/or Konqueror.
I can go into settings and change my desired filemanager if I click on a folder shortcut it will be opened with the filemanager I chose.
See how you go, regards Glenn