I use a 4-port KVM switch to connect one (Keyboard-Video-Mouse) to four computers. When I want to switch to computer #3, I just type Ctrl-Alt-Shift, then 3, then Enter.
You only need the 2-port version, unless you may get one or two more computers, or a laptop. Very handy for using a large monitor and keyboard on a teeny laptop!
There are many KVM switch choices, from $35 to $200.
http://www.buy.com/retail/computers/category.asp?loc=418&searchitemnumber=kvm%20switch
Belkin is the high-quality brand for a bit more money, though I've used a no-name brand for the last six years.
Check if your favorite keyboard and mouse are PS-2 style (1/4-inch circular plug) or USB style (3/8-inch wide flat plug).
Check the back of your computer also, though most computers in the last four years support both.
Most KVM switches use PS-2 connectors.
Technically, it does not *have* to support USB
because you can always get a little 2-inch adaptor to change
a USB keyboard into PS-2.
NETWORK
The best way to handle printing to connect it directly to one computer, then run a network cable to the other computer. Once the printer is working okay on one computer, select "My Computer", right-click on the printer, and select "Sharing...". You share the printer exactly the same way you share your C: drive. Just ask for more details if you don't know how.
With only two computers, get one "crossover cable" that goes directly from one computer to the other. It looks like a regular network cable (like a phone cable with a wider 8-pin connector instead of just 4-pins).
With three or more computers, get a $40 router (LinkSys and D-Link sell most of them) and connect each computer to the router.
Nice thing about a network is you can copy files from one computer to the other very quickly. I copy important files onto two or three different hard drives every day, just for additional safety backup.
Glad to help if I can, with any specific questions.