That printer, the HP Officejet 7400, has built in 802.11g access, in other words, it will act like it's own print server. So no need for one of those.
You will need the Streaming media device MDS mentions. That Squeezebox Transporter is drool worthy material
. I use my Xbox 360 to stream music to my reciever, which works ok for me, because I listen to more DVD-A and SACD's, and CD's than I play ripped material.