How many versions of the domain do you have to register to be covered legally? like .com, .net .ws .cc etc etc? Does anyone know?
None. Registering domain names doesn't bestow legality in any shape or form. But if you really mean how many domain names you need to prevent someone from registering one and possibly getting a free ride on your trademark rights, that depends on how much you're willing to invest in protecting your "brand".
i just buy the .com and I check to see if someone has grabbed the .net .org versions of the domain and check out the site just to see if they are alike in any kind of way
Get a trademark for the name. But just because you register a .com and trademark it, and somebody registers a .net or whatever, they can still get away with it if their use is "fair use".
Visiting the US Copyright Office you can find further reading on this. There is no way to protect a domain name unless you regiser such name as a trademark and for extended protection copyright your site's content.