Assuming that both PCs are connected to a router (which is a fair bet), you can simply connect the printer to one of them and share it over the network.
You haven't given much detail about your system, but for XP:
At each computer, right-click My Computer and choose properties
Go to the Computer Name tab and check that they are both members of the same workgroup. If not, click the Change button on one of them, and change its workgroup to match that of the other (You may need to restart afterwards)
At the computer to which the printer is connected: Right-click the printer and choose sharing. Select "Share this printer" and give it a name.
At the other computer open "My Network Places"
Double -click Entire network
Double-click Microsoft Windows Network
Double-click the name that you gave your workgroup
Double-click the name of the computer to which the printer is connected
Right-click the shared printer and choose connect
Set it to be the default printer for this machine.
The above may seem a bit longt-winded, but you only have to do it once.