Current:H1B with company A(Started:Oct,2010,expire:Sep,2011), this is my first H1B, I was on OPT before that.
Company A: Filed H1B extension in Apr 2011 and has gotten a three year approval on the new LCA for me. Now is going to file the petition.
Company B: Sent me a job offer which I have accepted. Now they are preparing my H1B transfer.

Question:
1.Will there be any conflict between my H1B extension with company A and H1B transfer with company B?
2.If company B starts filing the H1B transfer petition now, when should I be able to start working for this company?
3.Is there any potential problem for me to move from company A to company B in my case?