Oh yeah, of course that's what I was trying to remember. Quoting is different on DOS boxes. Try this instead:

perl -e "system(\"rsh hostname -l username -n \"touch test\"\")"
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From memory (sorry I don't have a Windows box to test on), single quotes don't work very well in the MSDOS prompt. So you need to use double quotes instead. And then you need to escape the double quotes inside the double quotes, or else use single quotes which Perl can handle:

perl -e "system('rsh hostname -l username -n \'touch test\'')"
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