NCTI offers home study courses in the feild such as Broadband digital Installer, computers and Broadband modems, Troubleshooting Advanced Services. The Installer course for cable installation would be helpful also. If you contract out to install modems you will most likely be adding digital boxes to users CPE. If you're looking for in-house work, these courses will make you a shoo-in. ncti.com is the site.
Good luck.