The problem with your original code is probably that the require Expect is failing so it never gets to the require Win32::Setupsup. For an easy fix, put the two in separate evals.

Or you can say:

use if $^O=~/Win/, "Win32::Setupsup";
use if $^O!~/Win/, "Expect";
[download]

IIRC, if.pm is in every perl version > 5.6.1 except 5.8.0, and is also available from cpan.

Update: I noticed a couple of posts saying /^Win/, which is wrong:

$ fgrep osname= hints/*.sh */config*
hints/epix.sh:osname='epix2'
hints/linux.sh:# The DR2 of MkLinux (osname=linux,archname=ppc-linux) 
+may need
hints/mpeix.sh:osname='mpeix'
hints/os400.sh:    osname=aix
hints/qnx.sh:  *) osname='nto'
Cross/config.sh-arm-linux:osname='linux'
NetWare/config.wc:osname='NetWare'
Porting/config.sh:osname='dec_osf'
epoc/config.sh:osname='epoc'
plan9/config_sh.sample:osname='plan9'
win32/config.bc:osname='MSWin32'
win32/config.gc:osname='MSWin32'
win32/config.vc:osname='MSWin32'
win32/config.vc64:osname='MSWin32'
wince/config.ce:osname='MSWin32'
[download]

It is MSWin32 (even on 64-bit windows, I think).