I have a 4 port Linksys router. Although it is probably 5 or 6 years old, it still works great. I need more ports in the the house, and don't want to go wireless.
Can I buy an 8 or 12 port switch, and connect it to the router?
If I do, will I still be at 100mpbs, or will I drop down to 10mpbs if I use a switch?
Can I just run one wire from the router to the switch, and then have all my connections go from the switch to the various wall outlets in the house? I have a mess already, so I'd like to keep it fairly organized.
As long as you buy a switch capable of 100mpbs, which all current models are capable of. If I were you I'd buy a gigabit (1000mbps) switch so that you are ready for future expansion, rather than investing in old technology. If you replace the router with a gigabit router you might end up with a much faster network, but keep in mind that PCI is still a bottleneck for gigabit ethernet, so to get the full speed you'll need a motherboard with built-in gigabit ethernet (dont even consider usb).
Yes, and a switch is much better than a hub, because hubs are stupid, switches are smart (hubs send all packets on all ports, leaving it to the devices connected to the ports to reject packets with wrong addresses. Switches, on the other hand, only send packets to the port with the device with the correct address attatched to it). In other words, far fewer collisions occur with switches than with hubs, thus, faster, more reliable connections. Routers are usually hub topology, not switches, or at least, they were up until recently, and I suspect many still are. So taking a single line out of your router to a switch and then splitting off the switch to your networked devices is actually a much better network topology than if you were to run all your devices off the router's ports.