I believe that doing both is a good idea. If you do not want to do a biz plan, then write down your goals and how you attained them. You don`t want to rush into anything, so make sure that you research your market and plan it out on paper before "going live" with anything.
I agree with the posts of doing both at the same time.
The Business Plan is mostly a theoretical document created for you to follow. When you’ve finished the first version (before your business is actually up and running) realize that it won’t be the last version. As mentioned earlier, it’s a “living” document
A website is almost like a mini-business plan, but in a fast-forward environment. The website is going to reflect much of what your business plan represents. The website is a practical, real, physical and brings to life what you have proposed in the business plan.
I always found it comforting that I could change the mock-up of my website as I make major changes to my business plan. Seeing the website helped to me visualize the ideas of the business plans and put them in to a real context.
Happy New Year and good luck the WWW and BP!