Im using a router that I had laying around to connect my PC to my squeezebox with ethernet cable. Can I use a crossover cable without a router to connect my PC to my squeezebox?
Yes, you can. If it's a fairly new PC, though, you might be able to use a standard ethernet cable. Most new network cards and chipsets utilize auto-MDX, where they'll internally cross over the connection if they can't at first connect to the device at the other end. If you post the PC model and/or network card, we could look it up.
If you config both the PC and the Squeezebox to use DHCP for getting a network address, then it should work without touching any network settings. In the absence of a DHCP server, each of them will auto-configure their network settings (APIPA -Automatic Private IP Addressing) to an address in the 169.254.0.0/255.255.0.0 range. The only real downside to this is that the Squeezebox may take an extra 15 seconds or so to boot up.