Replicating the Win Vista/7 program data paths did not work on an XP system; not too surprised as it was a long shot to be gin with. However a quick hard drive search did uncover the cache path for XP based installs.
The path to the Battle.net cache on an XP system is as follows:
C:\Documents and Settings\All Users\Application Data\Blizzard Entertainment\Battle.net\Cache
And for reference the same path on a Vista/7 system is as follows:
Program Data/Blizzard Entertainment/Battle.net/Cache
The solution is to either delete the Battle.net cache entirely and allow the game to try and recreate it on next launch or replace the Battle.net cache with one from a functioning installation, a copy of which can be found at the link below.
Working Battle.net Cache