I have a Linksys 10/100 8-Port workgroup switch. Model EZXS88W. Can I use this to hook up 2 computers to the internet at the same time or do i need a router?

Aditional Info:
Comcast internet
1st Comp Vista 2nd Xp
using a toshiba modem from comcast…
if theres anything else you need to know ask…