Where to start in this field?

I'm a firm believer that the best way to learn is by doing.  If you're just looking for a place to start, try and get on at a big box retailer, like Circuit or Best Buy.  You're 29, so you've probably done a fair share of work on cars (maybe built the "deep red" '34 alluded to in your login- got pics?).  Consider ordering a Basic and maybe First Class Installer study guides.  Look here: http://www.amazon.com/exec/obidos/ASIN/1588870030/the12voltcom-20, http://www.amazon.com/exec/obidos/ASIN/1588870022/the12voltcom-20

You can also take the MECP online practice test at http://members.ce.org/certifications/mecp/exam/practice/basicinstall.asp?ID=2322307

Be sure you know ohm's law, and you should pass the basic test no problem.  You can get more info here: http://www.ce.org/Training/MECP/119.asp

MECP is not necessarily required for a start, and neither is schooling, but it shows initiative and can help you get a start if you don't have experience.

I'm in the Dallas area, and have never heard of the school above.  That doesn't mean it's not good, but there's no real info on what is entailed- length of course, accomodations, etc.  I'm sure you can contact them for info if you wanted to, but in my opinion, you're money could be better spent on a nice system.  You could start installing your own gear or stuff for family and friends.

My brother graduated from ACU.  Unfortunately, I'm not sure where you would have to go- maybe small independent shops, but those usually want someone who's experienced.  I don't do this for a living anymore, it's just a hobby.  Actually, I work maintenance at a health care facility. 

I guess all I can suggest is to start reading- maybe pick up one of those study guides, and start absorbing the info that's contained inside.  Also, read up here as much as you can, and check out www.bcae1.com.  Other than that, start installing on the side if you can.  Again, I believe in learning by doing.  Work on your own car doing simple things like head units, and speakers.  As you get more and more comfortable, ask friends or family if they want you to do theirs, and just go from there.  This may be the best way for you to get experience in your current situation.