My husband is a H-1 visa holder, since a year and his company has sponsored his green card 4 months back. I am a H4 visa holder, I would want know , how soon will it be since I can start working.

Not enough information. What did they file 4 months ago? What EB preference category?

If they started the permanent residency process through labor certification (EB-3 for most H-1B's) for him 4 months ago, that usually takes about 6-8 months for approval. The I-140 takes about 6 months, and the current backlog for most countries is December 2005, and it takes 3 months after filing to get your EAD as a dependent spouse.

So, about 7-8 years from the date they start.