How do you test that your website can handle a certain load? Currently the website I handle sees around 120,000 active users a day. Half the site is marketing pages (mostly static HTML) and everything after login is dynamically generated.
for static stuff you can offload to cdn. where is session being stored? if it's on the web server you need to store it on the client or the database. then you can add more webservers. to test scaling at different numbers of users you need to profile your users work and then script it with a something like loadrunner against a test server.