Capacity Planning

Hello,
Designing a web site is becoming routine, but designing a web site to handle or process a certain load (# of users) being requested from your web site is demanding.

Example: during the “World Series”, their ticket servers crashed due to the demand of tickets.

Now a company or organization (“World Series”) with a “healthy” amount of resources was not able to design, configure & build a site for their demand. How does an average consultant/person go about designing an enviroment to handle its customers demand or requirements??? Is the a process,
“step-by-step” guide to deal with this issue???
Is there a way to design & configure a site to handle a ~25% – 30% increase in site demand???

Let me know…