I am thinking of purchasing B-Quiet. My 2000 Civic HB Makes a lot and i mean a lot of noise. Would this help a lot or just a little?

 

It'll help, the two trouble zones you'll want to tackle first is the doors, and the rear wheelwells from the inside.

B-quiet is good, but there are products that perform just as well, contstructed very similar (butyl based), and cost less.
b-quiet ultimate (60mil)(0.35lb/sqft) 50sq.ft: $129
edead v1SE2 (60mil)(0.50lb/sqft) 50sq.ft: $80
b-quiet exterme (45mil)(0.30lb/sqft) 50sq.ft: $84.99
edead v1 (45mil)(0.40lb/sqft) 50sq.ft: $50.00

Yes you can save some weight by going with b-quiet, but I think that if a product has a higher density with the same thickness, it will have more mass to absorb things.