I looked at the solutions to one book and it was in Microsoft Word format. PDFs are also available or can be generated from the Word docs.
I emailed OpenStax CNX (Not sure how related to OpenStax) and asked them how WebAssign did this. The person said WebAssign didn't get the exercises in any special format.
I was really hoping they used Latex. I don't suppose you have any brilliant suggestions for porting from Word to Latex or PGML including images and equations? ;)
The TEXT could be somewhat easily scraped from the PDFs. What would be nice is some way to automate the porting of the images and equations if that was possible to avoid introducing errors.
Any suggestions welcomed.