Need Help: Can I have both L1B an H4B stamped against my passport

[destiny]

Hi,

My husband is working in US on H1B (starting Oct 2012) and I am working here in India but having H4B visa stamped already. Now, my current employer is applying L1B visa for me. But before going ahead with all the paper work I just want to know answers for few of my questions:

1. My L1B travel dates are between Dec 2012 and Mar 2013 and its work visa so in that case will I be having both L1B and H4 visa or my H4 will get cancelled...or I can have both and while entering US it will be either on H4 or L1B.

As my project might get extended but if not then I intend to join my husband in US on H4B visa itself in June 2013.?

2. If my travel date are just for 5 months then does my L1-B is valid only for that duration or till 3 years.?

Please suggest what should I do? I am very much confused...

thanks

-destiny