$msg = MIME::Lite->new(
                To      =>$ToEmail,
                From    =>$FromName,
                Subject =>$Subject,
                Type    =>'multipart/related'
        );

        $msg->attach(
                ##############################
                # Called HTML script here... #
                ##############################
                 {open (my $fh,"<","sample.html" ) or die $!; local $/
+=undef; <$fh>}

        );

        $msg->attach(
                Type => 'image/gif',
                Id   => "$Attachment",
                Path => "$Attachment"
        );
[download]

is it correct ?

Not quite.

First of all, I feel it needs to be said that HTML is not a scripting language. It is a markup language.

Next, your open() statement will never work. Why? Because you can't put it in a hashref like that, and still get your expected result. You may also want to see the documentation for MIME::Lite.
Instead, use something like the following:

$msg->attach(
    Type => "text/html",
    Id => "sample.html",
    Path => "/path/to/sample.html"
);
[download]

...which should save you some hassle with the files.

I hope that solves(or at least helps) your question, although I do highly advise you to read perlintro, among others.

~Thomas~ 

"Excuse me for butting in, but I'm interrupt-driven..."