negotiation questions

[btmagnetw]

some basic questions about negotiation. i have two offers i'm considering.. one is ~$3,000 more than the other. the company i am leaning toward is the one that pays less.

how do i negotiate a higher salary? do i propose it to the HR contact or to someone else? do i mention the offer of the other company? do i propose another amount or do i just say if they can match it?

this is for an internship and i don't know if salary negotiations are common. i wasn't even going to do anything until i heard from a friend that he was going to negotiate as well.