SQL 2008 r2 in SBS 2011??

hi,

can any1 tell me how you can get SQL 2008 server on a SBS 2011 standard.

i basically need SBS 2011 for 8 employees and need to have windows SQL  2008 r2 server running on it.

I just cant get my hand around the basic info on the microsoft website that you purchase SBS 2011 with 5 Cals then you purchase sbs 2011 premium add on and that give you SQL server???

or

you have to purchase windows SQL server 2008 r2?

What would be the way to do it by purchasing SBS 2011 and then what for 8 empolyees?

greatful if some1 could get back to me.