I used a wireless connection most of the time on that computer. A wired connection wasn't possible for some time because my router was on the other end of the house. My PCI slots are empty except for my video card and sound card (i think that's what it is anyway.)
Did you have a USB dongle sticking in a port on the back of the motherboard? If not, you will need to get one. Newegg has THIS ONE
on sale for $14.99 FS with code EMCXTXM88 if you are in the US.
Take a look at the sound card; what is the brand and model?