a file name with space for http

my Ruby 1.6.5 platform is "i386-cygwin" on windows 98

i have a trouble for downloading a file using http protocol, like
response , = http.get( "#{FILE_NAME}" )

one web site has a file name with space in the name.
how to change the space?
I tried "file name" and "file%20name" which is used in browser,
but it failed.

cheers,
sungjin moon
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