You can make FF/IE not send the HTTP Host: header by using the IP address of your website. Other options are to use either a program meant to do that sort of thing (e.g., a perl script), or do it manually.
For the manual process, do something like fire up Hyperterminal, connect to your-site.example.com, port 80, turn on local echo (so you can see what you're doing), and type in the HTTP request. e.g.,
GET / HTTP/1.0<return> <return> or GET /your/page.html HTTP/1.0<return> Host: happy.days.are.here.again<return> <return> You'll then get to see the entire response from your webserver, headers and all.