>Does having a static IP make any difference to using a router? 

Yes, but mainly in how the router needs to be configured. Most routers are made to work with static or dynamic IP addresses. 

>What is the difference between a public IP address and a static IP address? 

The types of IP addresses to compare are: 

1) Public, which is contrasted to private. 

2) Static, which is contrasted with dynamic. 

Let's look at them in that order. 

Most IP addresses are public. All that means is that they are accessible from the internet in general. Certain ranges of IP addresses have been designated by convention to be private, or not addressable (routable) from the internet. This is so that these addresses can be used on anyone's lan (Local Area Network) without conflicting with anyone else's use of them and without using up the finite number of routable IP addresses available with the current numbering scheme. 

	 :	The Internet Assigned Numbers Authority (IANA) has reserved the
	 :	following three blocks of the IP address space for private internets: 
	 :	10.0.0.0  - 10.255.255.255  
	 :	172.16.0.0 - 172.31.255.255 
	 :	192.168.0.0 - 192.168.255.255  


(I copied the above indented bit from http://www.isi.edu/in-notes/rfc1918.txt (slightly edited to get rid of parts that are not necessary for our current discussion) because I couldn't think of a better way of showing which ranges are private. 

Any IP address not designated as private is public. 

OK, that's that part. Static vs Dynamic next. 

First of all, whether an address is public or private says nothing about whether it is static or dynamic. 

This section should be a bit simpler, as the terms are fairly self-explanatory. Basically, a static (or fixed) IP address is one that doesn't change. If you have a static IP address, you always have the same IP address. 

A dynamic IP address does change. Generally folks on dialup have dynamic IP addresses - each time they dial in, they get assigned an IP address (at random, or following some scheme) by their ISP. People on Pacbell's current basic DSL plan also have dynamic IP addresses. Pacbell basic DSL uses a service called PPPoE to log in, and, like dialup users, each time they log in, they get assigned an IP address from a pool of addresses. 

You mentioned in an earlier posting that you have Pacbell's enhanced DSL. That means that you have 5 static (public) IP addresses. 

What a router will do is allow you to put some (or all) of your machines on private IP addresses so that you don't need to buy more addresses from Pacbell. 

-- Russ