I seriously doubt that the Oracle Client software will understand Cygwin paths, and it certainly won't be certified (so don't expect any help from Oracle). The path to the Oracle EXEs isn't generally set in the ORACLE_HOME env var on Windows boxes (maybe that's not with XP, but certainly for W2K & NT4), but in the PATH. Try putting the WinXP path to your Oracle software in the %PATH% and then fire up Cygwin's Perl installer, eg
set PATH=c:\Oracle\dev_suite\bin;%PATH%
(remember the "bin" at the end of the Oracle PATH)
