I'm not sure why that doesn't work. I will recommened against using the & notation if at all possible. The following works for me (cygwin 5.8).

$foo=5;
sub has {print "ok\n"}
sub hasnt {print "no dice\n"}

eval "require $foo" ? has : hasnt
[download]

prints ok

$foo="nosuchmodule";
sub has {print "ok\n"}
sub hasnt {print "no dice\n"}

eval "require $foo" ? has : hasnt
[download]

prints no dice