You can avoid the command shell altogether, if start is an exe or com file:

  system (qw[start http://www.foo.com/cgi-bin/foo.cgi?a=2&b=3]);
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But something tells me that start is a built-in to cmd.exe, so you'll still need it. In which case, quotes are your friend:

  system q[start "http://www.foo.com/cgi-bin/foo.cgi?a=2&b=3"];
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Hope that helps.

Update: D'oh - too slow. :-)