i had this problem too. it really did do my head in. re-run the network setup wizard on all your computers. also reset your router if that doesn't help.
keep doing it. also, make sure no programs are running when you run the network setup wizard, and restart immediatly when requested. not later on.
as far as IP addresses are, stick to using DCHP, all your IP's will be assigned automatically. it is easier and more reliable. (and faster)
i assume you are talking about a workgroup network here, and not a domain one.
also, if you don't smoke, i suggest you start. and have a bottle of vodka to hand.
computers often take the p!ss and it can sometimes take ages to sort out.
another also is make sure the workgroup name is the same for all computers.
i use my address. example: 22_ROSEFIELD_AVE
p.s. that aint my address, just an example of a workgroup name.
good luck, you'll need it.