How do you go about starting a stock photography company?

[Lauren]

I've got a camera and the niche target market but I'm not sure about what sort of business registration or tax ID type things I need. Are there any other sort of legal things that need to get filed?

[Silvatungfox]

You fail to mention any photographic training. Stock photography is a big business and before you go to the expense of starting your own company which will need a good web site, tax id, promotional budget, business license, business plan etc, perhaps you should see if your stuff will sell.
this is my shutterpoint page
http://www.shutterpoint.com/Photos-Brows...SILVASPOON
(I am sure it will but if you have a client base first it will help you immensely.) Might I suggest you get free accounts at the current stock photo sites and test the waters? Shutterpoint is a pretty good one to start with although there are some limitations on how many photos you can post unless you pay a fee.
this is my photo & travel web site
http://www.silvaspoon.net/
I also design and put together websites like the silvaspoon one.
There will also be getting your web site onto the search engines which takes some time and effort.. I have a program to analyze and make suggestions to increase your ranking in the search engines..
Until you declare yourself a business your social security number can act as your tax id.. depending on your location your business license can come later when you know you have an income to pay the annual renewal fees and company taxes as well as personal taxes. (you as a freelancer just declare your income on your tax return)
There are a number of other places to put your stock photos out there for sale that already have people coming to their site to find what you are going to sell, so I would do a search and list with as many of them as you are able to.(some will require some submissions to judge if they think your work is good enough to sell.)
I also do a photography blog
Is your current work anywhere to have a look at?
Good luck in your new business either way. (as in going with established sites first or opening your own)