X12 standards are published by the Washington Publishing Company . Implementation guides were subsidized by CMS, but this was completed in April 2006. The PDF version of the implementation guide is $ 175. If you decide to download it, make sure you get a combined version that includes the original standards and additions. The current version is 4010A. Version 5010 will be required from January 1, 2012.
I don't know what your situation is, but I found that a health complaint is one of the most complex EDI transactions. I have always used special display tools such as Gentran or ECMap, which are specially designed to facilitate the conversion of X12 files to many other formats and vice versa. Another important ability of EDI translators is that most of them can check the consistency of your X12 files.
Outgoing files are a bit simpler as you control the data. I recall creating test files with C programs in a UNIX window when none of our trading partners was ready to send us test data. However, I would not recommend this as a long-term solution. You can consider the information exchange center, but if you decide to do it yourself, you really need standards and implementation guidance from each of your trading partners.
Good luck