H1B Transfer during 6th Year

[raogk]

Hi, I am on H1B visa since Dec, 29, 1999 (arrival date) continuously and working for a company. My company filed for Green Card last year and labor condition is still pending as with current retrograce. Now my 6th year ends by Dec 28, 2005 so my employer filing for 7th year extension. In this context, my current client is interested in hiring me. What are the possibilities that I can be employed with client but do not go out of status? I ask this question with assumption that we cannot change employers when 7th year extension is about to come? To ask more details, is it possible to transfer H1 once 7th year is approved as Green Card is for future employment?
thanks in advance!!!