Muthu,
I don't think you are going to see your approval in May 2004. Lot of Sept, Oct, Nov cases are still pending. It is O.K, that you are not getting salary as mentioned. Your company can always say that after getting Greencard, they will give you the salary mentioned in the LC.
You cannot change job before 180 days from your I-1485 filing date. After 180 days, If you are loosing your project/Job due to the fact that I-140 is not approved, then just use AC21 to save it. But there is very high risk. If your sponsor company is willing to take care of any RFEs, it will be some what safe. Another thing is only Sept cases are getting RFEs,. Your case is filed in December and may be some officer with Common sense process your case and you won't even get RFE.
As per law you may change your employer after 180 days, even before your I-140 approval. But RFE should be taken care properly, if comes. I have confirmed this with few attorneys.
I am not a lawyer. So discuss with your attorney for proper advise.
nanshi.