There is no size difference with the chips.
But while Im talking, I STRONGLY recommend upgrading the ram yourself.
8GBs of Ram is $244.99 and it takes just a few minutes to install it yourself. Just remember when buying RAM that it uses laptop RAM, not Desktop RAM
If you want, you will be able to sell the 2GB of MacMini RAM for about $40 on eBay. You can get the screw driver you need for $1 there was well,
The net cost of doing it yourself is $200. Apple will charge you $300 more than doing it yourself. You could buy an iPhone 4 and have a $100 to make it rain in the club. (jk)
Wait a week or so for a tutorial on how to change the newer Mac Mini Ram comes out though.
(I read this and assumed he was going to pay the $500. It never crossed my mind that he was asking about the size of the chip so he could do it himself. I am retarded :)