Two networking questions

[JohnE]

I have two networking questions (both unrelated).

1) From my limited understanding of networking, I gather that one PC on the network is usually set up to dish out IP addresses, whereas the others are all set to obtain an IP address automatically (there's a special name for the IP address server - but I can't remember what it is). Here's question 1 - what are the rules for 'assigning' this special address server? I've noticed that certain IP addresses seem to configure themselves as a server automatically. For example, 169.254.0.1 works as an address server whereas 169.254.0.2 doesn't. Similarly 192.168.0.1 works but 192.169.0.1 doesn't. What are the actual rules?

2) I've noticed that a lot of new computers have two onboard LANs (often a Gigabit LAN and a 10/100). Is this just so you can connect the PC to either type of network or could such a PC be used as a 'bridge' between two otherwise unconnected networks? If so, could one PC be a member of 2 workgroups or would this only be possible with domains? (I'm thinking of using a PC for just this purpose - to act as a link between 2 unconnected networks - so I'm just trying to find out what would be involved).