The & worked for me on XP so I assumed that it would work for you. Anyway, there are several modules that will create background processes for you on Windows NT/2K/XP platforms. Such as Proc::Background and Win32::Process on CPAN.

use Proc::Background;
my $proc = Proc::Background->new("C:\\Perl\\bin\\perl.exe generate_rep
+ort.pl");
[download]

Will kick off a background process via Win32::Process, instead of relying on the shell to create a background process.