The fact that you have two computers to work with will allow to do quite a bit in terms of 'gettting your hands dirty' doing a wide array of network administration tasks.
When I started, I simpy got my hands on a well rounded networking / admin book and worked through each of the chapters, slowly building a very small, two computer network in my home.
Once the network is up, you can do the following sorts of things without having to even deal with dial-up concerns:
1. NFS
2. NIS
3. RAID
4. Samba
5. Apache
6. Logical Volume Management
7. Router Setup and Configuration
8. Firewall Setup and Configuration
9. Virtual Network Computing
The list goes on........
Eventually you shoudl try to get your hands on a third system to really tap into router and firewall use if you dont configure your dial-up. You can try hacking and tweaking your own network to see how things really relate to each other and test your skills on a regular basis.
Basically, you dont need Internet access to begin the journey into administration with Linux.
I used/use the following book to get a good feel for Linux admin capabilities:
Linux Administration: A Beginners Guide Second Edition
Publisher: Osbourne
This book is designed to simply get you up and running with a basic understanding of the concepts presented. I found/find it to be VERY helpful.
Also use the Linux HOW-TO's at
www.linux.com as often as possible to reinforce or supplement your readings.
Good luck