FHWA has a publication "Micropile Design & Construction Gudelines" Publication number FHWA-SA-97-070. It will give you a good background in the subject. Ithink it can be downloaded from the FHWA website.
DWIDAG-Systems has a very good proprietary micropile called GEWI Piles. We're using them for our latest project with very good results thus far. Their website is: