fork and exec, despite the heroic efforts of a number of people, don't really work on Win32 platforms. You're much better off using Perl's Win32 interface. Something like the following will get you on your way:

use Win32;
use Win32::Process;

my $ie;
Win32::Process::Create(
    $ie,
    'C:/Program Files/Internet Explorer/iexplore.exe',
    'http://localhost/foo.html',
    0,
    NORMAL_PRIORITY_CLASS,
    '.'
) or print Win32::GetLastError();
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Needless to say, this won't run on Unix, but if you are careful you can encapsulate this, and do the Right Thing according to platform.