Okay, do you have a windows machine, or a unix/linux machine? If windows, then you'll use a windows path (e.g. c:\temp). If linux, you'll use a unix-style path (e.g. /tmp).
This directory is where PHP will store all the active session data, so you need to make sure the directory you specify exists and that PHP has access to read and write files in that directory.
Take care,
Nik
http://www.bigaction.org/