What are the travel regulations for a UK citizen wishing to visit the US from Mexico?

So I'm flying out to live in Playa Del Carmen for a while in about a month's time. Being the internationally socail guy that I am though, I have a lot of good friends in the US that I would like to visit while I'm in Mexico.
I've been told by my family out there that at the moment, the US Government does not permit travel INTO the US unless you have a return ticket to your country of origin.
Is this true? As I'm planning on staying more than 6 months, is there any way around this?
There's also a possibility I might be able to be signed into my family's business while I'm there and get some kind of imigration papers sorted.

Any help would be greatly appreciated.
Ahh sorry, I think there might have been a little confusion. I'll be residing in Mexico where my family is, not the US.

I'd like to fly from mexico when I'm there, visit my friends in the US for a few weeks, then fly BACK to Mexico and stay there.

The Visa Waiver Program requires that you have a return ticket to "any foreign destination", but not to your home country.

Also, you can only visit the USA under the VWP for up to 90 days. You have to leave North America as going to Canada Mexico, and many Caribbean Islands does not count as "leaving the USA", There is no specific time away required by the VWP and you theoretically could return the next day for another 90 days. However, you have to convince ther Immigration Officer you really are visiting and are not using the VWP to illegally reside in the USA.

Given that you plan to stay in the USA for more than 90 days you should go ahead and apply for a visa. You should also be able to visit the USA on the VWP while your visa application is processed.

Warning: ACACHRIS is NOT correct. The Visa Waiver Program has rules and you CANNOT simply "fly into the US and back to Mexico at will". Check the rules via the State Department website.

Good luck!

If you have a valid U.K.passport you can fly into the US and back to Mexico at will.
What you have heard is NOT correct.
Keep in mind not to overstay your F.M.T. visa. They are good for 180 days. You can exit Mexico for one day a re-enter for another 180 days and do this indefinitely.
If you are in southern Mexico you can go to Belize or Guatemala.

P.S When you fly --take your visa and surrender it even if you have 4 months left on it. They are quite sticky about those issues
I am a Brit and have a passport (U.K) and am never asked to return to England or my permanent resident card(Canadian) but rather treated as a Brit