Call me crazy, but I just made some objects so that you can get the info from /etc/passwd and /etc/group, and convert between UIDs/GIDs and usernames/groupnames. Its part of my effort to provide as many low level primitives within Pd as possible. Or really, its make a libc interface for Pd.
http://at.or.at/hans/pd/objects.html
Of course, these will be included in the next Pd-extended release. I haven't touched Windows yet, but I plan on it.
.hc
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Man has survived hitherto because he was too ignorant to know how to realize his wishes. Now that he can realize them, he must either change them, or perish. -William Carlos Williams