Would really appreciate the answers

I had two offers from the company A and B. Both the companies have processed my H1. Right now I am working on OPT with the company A. Company B asked me to join from oct 1 2005.

-Is there any legal hassles that I would need to face if i will leave company A. I have not signed any legal documents as to have a bond with the company.

- d0 I need to pay the H1 visa fees when i leave??? contract doesn;t specify. I have the H1 papers in hand that are approved from co A

- Do i have to join right away the company B on oct 1 2005 ?? or can i join after a month's time if they give me permission to do so.

- If i join the company B on oct 1 2005, does that automatically make my first h1 from co. A invalid

- Does all this would affect future green card processing ???

I would appreciate all the advices and suggestions on these questions. Thank you