Just wanted to add - if all you want are accommodations such as word processing, more time, dictating as needed, these can be given under a 504 plan. Generally speaking, a 504 plan does not provide the same level of protection as an IEP, and does not give you the procedural safegaurds that an IEP provides, but it is a way to document that your son needs certain supports (not modifications or instruction) to access the curriculum.

Again Wrightslaw is a great resource to learn more about 504. Here are some links that may help:
Understanding the Differences Between IDEA and Section 504 http://www.ldonline.org/article/6086
http://www.ldonline.org/indepth/accommodations
IEP/504 Similarities and Differences http://www.wrightslaw.com/advoc/articles/504_IDEA_Rosenfeld.html
Generally speaking, an IEP offers more and if you can keep it, you'll be better off.