Okay, I remembered hearing about cygwin, but couldn't remember what it was, so I looked it up.
Found this:
Cygwin supports both Win32- and POSIX-style paths, where directory delimiters may be either forward or back slashes. UNC pathnames (starting with two slashes and a network name) are also supported.

You MAY be able to get by with using regular windows path names, from what I'm reading.

Having said that, there may be issues with other programs that know nothing about cygwin....rsh/rsync being a good example. However, I found in the cygwin API a function cygwin_conv_to_full_posix_path that"Converts a Win32 path to a POSIX path." Maybe that's what you're looking for?