Someone has already suggested Tannenbaum's book. "Computer Networks"
I worked for 3 years in a MS shop supporting MS systems for clients, I attended classes and earned my MSCE. All of the classes which I took for MS were centered around 'go to this menu' 'click this' 'entered this'. Yes I could set up networks, VPN's, servers, but I didn't really start learning the nuts and bolts until I started working for a company that supported Linux servers.
Once you understand the basics from Tannenbaum's book then you might go to 'Wireshark Network Analysis' by Laura Chappell.
If you have time go to 'Linux Firewalls' I used Ziegler's book, but there are a number of sources. On your network you may want to try and setup a muilti-homed linux system protecting a linux system. You can learn a lot about how a computer handles packets by setting up a server with iptables and adjusting it to allow certain packets or to allow only certain services. Also look at studying Computer security and security tools.
Switches, You should look for switches that will allow you to monitor ports on the switch. If you only have a 100 computers on your network they may not allow you to budget for a network analyst to come in and analyze your network if there is a problem.
Look for any tools, such as Snort or installing a computer which can tap into your internet traffic, that will give you a raw eye onto what is happening on the network. Nothing is worse than having a network problem with multiple computers on the network and being blind.
You will still get to use your programming skills, there are few programs which offer exactly what you want or need to monitor your network and your computer systems. Eventually once you know more about what you want, then you can take results from other programs and craft your own system with reporting tools.
To prepare you for this, imagine you have just been given a new position within the company where the previous programmer has left the company. You have an application which he has built up and put into production over the last five years. You are now in charge and there are no comments on the code. Your first ethernet card failure will be like your first bug. Same for switches. No one told you they could fail like that. Welcome to Hell.