There have been times I have seen some networking questions on the boards here. Also as a student studying for my associates degree in Networking I have found the network simulation programs on this site (link below) to be very helpful. I have purchased both the CCNA & the CCNP versions in the last couple of weeks.
Both are very well thought out and easy to use. there are hundreds of labs that come with the programs to use while studying for the Cisco Certified Network Associate (CCNA) or Cisco Certified Network Professional (CCNP) exams, or if you are currently a student you can design and build your own lab assignment. For the network administrator, you can use it to design a new network or test possible upgrades to the current network for your employer.
There is a demo available for download but I do not know what functinality you get with the demo.
The CCNA version is $149.99
The CCNP version is $249.99
If you order the CCNA version they will give you 50% off the CCNP