In your local network your cable/DSL router or your AirPort box will probably be a DHCP server, handing out network addresses to devices that ask for one. It will have a range of network addresses that it hands out. We have to pick one outside that range, but inside the range of addresses that the router and/or Airport will recognise.
Addresses are four-part items. The first three parts define a Local Area Network, and the last part is a device address. So my laptop, at the time of writing, is 192.168.1.35: 35 is the device address, and 192.168.1 is the network. The router is 192.168.1.1 -- get it? First, find the address of your machine. If you are on OS X, look in your System Preferences, choose Network, choose whichever thingy says 'connected' in the list on the left-hand side -- possibly AirPort, possibly Ethernet -- and then click the Advanced button towards the bottom right. You'll see a window like this if you are using AirPort
and in that case click TCP/IP. If you are using Ethernet you will already be looking at the TCP/IP window
Notice 'Using DHCP'. If you don't see that, give up now and seek help. In this picture, my laptop's device address is 35, because after the IPv4 address it says 192.168.1.35. Probably the router won't give out big device addresses like 200 (the maximum is 255, but don't use that one!). So in this situation I'd guess 200, and I'd probably get away with it (I did). Always pick an address which has the same first three parts as the address which follows Router, then add the device number which you guessed. So in this case you could guess 192.168.1.200 as the print server address.