but might not be the ones you originally had in mind. As Bob points out, you can easily put the printer on a print server - either wireless or wired. You can also get a wireless base station that has an integral print server port in addition to a few wired ethernet ports, if your physical layout lends itself to the printer and the wireless base station being in the same place.
There are devices such as the one Bob noted that seem to be external hard drives but more correctly defined are network attached storage (NAS) devices. A plain vanilla USB or Firewire external drive must be connected to a host system where its operating system recognizes it as another drive letter. Sharing it with the rest of the network requires tweaking the O/S. The more sophisticated NAS drives have an embedded operating system (often a Linux variant) so they can be just plugged into an available ethernet port on the network, such as one of the wired ports on a wireless base station, and is available to every system on the network with very little further configuration needed.
For number 3, as Bob correctly points out, the iPod was not intended by Apple to be a network device. Even when docked to a host computer, it works only with that host. The solution is put a copy of your entire music library out on the NAS drive we talked about in #2 above. If you use the iTunes media player on your computer, you can have it build its library and playlists from the central repository of music files on the NAS drive. If your computer is a wireless laptop, the NAS drive remains accessible no matter where in your house you connect to your network from. Then, when you take your music on the road, you only need to worry about syncing your iPod with your master library on the network using the iTunes player.
Finally, to take it one step further now that you have a wireless network and an iTunes playlist based on the NAS drive, you can get an Apple Airport Express unit and configure it to be an audio input interface to your home stereo system and blast out your iTunes playlist on the stereo. From a wireless laptop, you'll retrieve the music file from the NAS drive, play it with the Airport selected as the output device, the laptop will send it back to the base station wirelessly and then the base station will send it to the Airport which is plugged in beside the stereo, and there will be a standard audio cable from the Airport to one of the stereo inputs.
have fun with it,