Construct raw strings?

[Thomas W]

I got a stupid problem; on my WinXP-box I want to scan the filesystem
and enter a  path to scan like this :

path_to_scan = 'd:\test_images'

This is used in a larger context and joined like

real_path_after_scanning = os.path.join(path_to_scan, somepart, 'foo',
'bar', filename)

Using os.path.exists(real_path_after_scanning) returns false. The
problem is that some of the parts being joined contains escape
characters, like \. If I take the seperate parts and join them using
the interpreter, like :
>>> f = r'd:\test_images\something\foo\bar\test.jpg'

it works ok and os.path.exists(f) returns True, but I cannot the that
r' in front using the os.path.join-method in my code.

I don't know if this makes any sense at all, but I'm lost. Damn those
stupid windows-paths !! 

Thanks in advance,
Thomas