Reversible replacement of whitespace characters with visible characters

[Micah]

Hi,

I'm looking for a tool to do the following 2 things:

1) Given a string (ie. file, std input, whatever), replace all
whitespace characters with visible characters (like their Unicode value
or something).  The end result will be one long unbroken line

2) Given a string altered as in step 1, "decode" it back to the
original string.

Note: The original string (it will usually be source files) might
already contain Unicode values, and these must remain and not be
altered in step 2.

Note 2: I'm working in a Windows XP environment, but I have access to
cygwin if that makes a difference.

Can anyone think of a tool that already does this?  I could probably
whip something up, but if there's already something that does it I'd
rather just use it.

Micah