Have a read of these:
http://www.thailandguru.com/thailand-co ... ation.html
http://www.retire-asia.com/thaibiz.shtml
http://www.stickmanbangkok.com/reader/reader567.html
http://www.boi.go.th/english/how/typica ... siness.asp
Found with a simple Google search so can't confirm their accuracy but there are also countless other sites out there with info on starting a business for foreigners in Thailand.
Things I've noticed changing in the last few years:
1) You now need photographic evidence of your four Thai staff members, their house papers, and bank accounts.
2) Restrictions on what you can actually do as "work" have increased.
3) You need to pay income tax on a minimum of 50k per month, and company tax on top of that.
4) You also have to pay national insurance for your staff.
5) More investigations and check ups on what you are doing.
6) Proof of shareholder meetings and their "dividends".
These are just a few that stick out now that didn't apply years ago, try comparing this lot to whats required to setup and run a Thai only company and you'll have a good laugh. I'm not trying to scare you off - just letting you know that its far from an easy ride. The general feeling that you get from the government and immigration is that they don't want foreigners working here, they only want tourists and retirees.
