<pre name="code" class="python">1. Regular Expression
^([a-zA-Z]:|\\\\[a-zA-Z0-9_.$ -]+\\[a-z0-9_.$ -]+)?((?:\\|^)(?:[^\\/:*?"<>|\r\n]+\\)+)

eg.
c:\folder\subfolder\file.ext

Extract:
\folder\subfolder\

\\server\share\folder\subfolder\file.ext

Extract:
\folder\subfolder\

2. Python code
import re
subject = 'c:\\folder\\subfolder\\file.ext'
match = re.search(r'^([a-zA-Z]:|\\\\[a-zA-Z0-9_.$ -]+\\[a-z0-9_.$ -]+)?((?:\\|^)(?:[^\\/:*?"<>|\r\n]+\\)+)', subject)
if match:
	result = match.group(2)
else:
	result = ""

print result,