I'll be the first to post the pessimist reply that the four hour workweek is not a reality if your primary goal is a four hour workweek. I suppose if you follow the exact steps in Tim's book and aim to create a product-based business where everything can be automated, then the 4 hour workweek is possible. But for virtually any other type of startup business, you'll likely find yourself fully engaged and working long hours to run the business.
Maria and Anup both have great points - automate and delegate as much as possible. This is key to running any business and probably the best advice to effectively lessen your involvement in day to day operations. I've found personally that if I try to distance myself too much, the business suffers. If you can count on reliable managers, employees, contractors to carry out the work for you, then you might be on your way to living the dream of the 4 hour workweek.
I suppose my point here, is that entrepreneurship is not that simple. Tim is a visionary and an idol, but we can't all live his dream.