Problem with popen on Windows

I am currently having troubles with the popen method on Windows (win
2k, ruby 1.7.3, mswin32 build). My code look like this:

cmd = "ruby -I. -Iso -Iredist -rplugins/Debugger/debuggee.rb std.rb"
f = IO.popen(command)

When running this piece of code I invariably get the following error:
ruby: no such file to load – plugins/Debugger/debuggee.rb (LoadError)

I have tried all sorts of things to fix the problem to no avail. I
have checked that the include path of the forked process was ok so it
should be able to find the file in question. Even putting the full
path name to debuggee.rb doesn’t solve the problem.

note that the exact same command run in the exact same context (same
file system) works ok on Linux.

It looks like the -r argument is not well understood.

Are there any specific things about popen on windows that I should be
aware of? (like special characters in the command line or whatever).

Any idea is welcome because I’m stuck

Thanks for your help