5.1 speakers not working on Vista 64

Hello,

I purchased the HP Pavilion Elite m9357c from Sam's club. I have two issues.
I cannot get 5.1 sound from my Logitech x-540 speakers... because of configuration issues (the hardware is working, i checked)
And i do not know which sound card is installed in the computer. I only know that "it's capable of 8-channel Hi-def. sound."
plz halp. thx