One question dont local ip address change when you log on and off the network etc.
Local addresses only change if you have a DHCP server assigning IP addresses. Routers can be configured to be DHCP servers, or you can configure a linux box to be a DHCP server. The lan will work with a DHCP server or you can assign IP addresses. I'm running DHCP, and my router is the server. It usually assigns the same IP address to the same MAC address, but there are no guarantees. The advantage to DHCP is, if you are plugging in different machines to a lan, the user doesn't have to know and assign an IP address to get it working. The new box will make a DHCP request, and the server assigns an available IP address.
It may be easier for you if the number of machines is small, and not changing to assign the IP addresses manually. That will get rid of the guess work until you resolve any other issues.
In linux, the easiest?? way to tell what your IP address is; at a console type /sbin/ifconfig example:
eth0 Link encap:Ethernet HWaddr 00
inet addr:192.168.1.13 Bcast:192.168.1.255 Mask:255.255.255.0
inet6 addr: fe80::2d0:b7ff:fe26:b378/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:314 errors:0 dropped:0 overruns:0 frame:0
TX packets:696 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:152306 (148.7 Kb) TX bytes:88023 (85.9 Kb)
Interrupt:11 Base address:0xe000
lo Link encap:Local Loopback
inet addr:127.0.0.1 Mask:255.0.0.0
inet6 addr: ::1/128 Scope:Host
UP LOOPBACK RUNNING MTU:16436 Metric:1
RX packets:185 errors:0 dropped:0 overruns:0 frame:0
TX packets:185 errors:0 dropped:0 overruns:0 carrier:0
RX bytes:17448 (17.0 Kb) TX bytes:17448 (17.0 Kb)
The MAC address is the field HWaddr. This is burned into the card by the manufacturer. The field inet addr is the IP address my machine is currently using.
Hope this helps.