Why does good Information Architecture matter for your site? Why can't you just start a few pages and drop in the content?
This may be a great way to get started. If you're chomping at the bit to get your thoughts out there, go ahead and start entering content. Just make sure to tag it and refine it over time. If your site holds information, you want to present that in as easy to consume format as possible.
Let's say you're working with a foundation. You want to show off their work to keep affiliates engaged and donations coming. You don't want visitors to leave wondering what your organizations does with the money - they'd rather donate where they can feel like they're making a difference.
How do you display content that matters to people?
Understand their desire and why they came to the site. Provide information that matches their intention, and combine it with other info that they may appreciate.
Good IA takes time to develop. You will have to put your best foot forward and see what the reaction is. Use analytics to see how users flow through the site, and keep asking if there are areas you can refine to make them more clear. Good IA is lean and gets the point across.
IA is Structure
The architecture you build allows content authors to fill the site over time. Bad architecture won't fit the needs of visitors, and there will be a disconnect with the author's intentions.