You can download the SDK that includes documentation and sample code from here:

na.sage.com/.../development-partners-erp-crm-hrms

Expand the program levels section and fill out the form to gain access to the download page.

If you download the SDK, I found that viewing and actually debugging the sample solution WinFormExample.sln really helps to understand what's going on. You'll need to do some reading of the documentation that comes with the SDK to help it make even more sense. There are some tricky things about application ID's and the peachtree.ini file that I had to figure out on my own but you should be able to manage it without too much hassle if you have an average .net or C# background.

I also found that setting up my own copy of Sage on my hard drive helped as opposed to sharing a development environment with other people. I check this board out every couple of days so feel free to message me. I'm no expert but I can do some basic stuff.