Can i use a 2004 Honda Civic AC compressor on a 2008 Honda Civic?

Can i use a 2004 Honda Civic AC compressor on a 2008 Honda Civic?

Don't count on it. Those are two completely different generations of car, and you haven't even clarified if they have the same engine.

Hope you understand that you don't just unbolt and replace an AC compressor. Opening that system without the equipment to capture/recycle any freon left in it is against the law. Additionally if you don't have the equipment to pull the new system down to a vacuum and purge it to dry it out prior to charging it with freon you are just wasting your time, effort and money. Without being at vacuum the system will not accept a full charge and will be saturated with moisture which will ruin the system.

Go to a Honda website and check the part numbers.

AC repair is not a DIY job. You need professional equipment to properly service the system.

Bernardi Parts
Acura Audi Honda
http://www.bernardiparts.com/Honda/Parts-Car.aspx

Nope, they are two completely different gens of Civics.