Tivo: I have a Series 2, which has a USB connector for the network connection. I got a Linksys USB network interface, plugged it in, and it was seen right away. The only difference between what you plan on doing is that mine is wired, whereas yours will be wireless, probably 802.11g. Install the Tivo software on one of your desktops, configure it to see your Tivo boxes (Tivo has the instructions) and you can copy shows between the PC and Tivo. If you have two Tivo boxes I believe you can copy them between the two. Other than the router (which you have) and the Tivo with networking cards (which you will get), and a PC with a networking card, you don't need anything else.
Printer: Go to the PC with the attached printer. Under the properties of the printer specify that you do want to share it. That will make the printer available to all other Windows computers on your network. This PC is now acting as a printserver. Go to another PC. Click on Add Printer under the Printers section. When asked if the printer is Local or Network, click on Network. Next screen has 3 options, Find a Printer / Type the Printer Name / Connect to a Printer on the Internet. Choose Type The Printer Name, but leave the box below it blank. Click on Next. Next screen, expand your network, expand the computer that has the printer, you should see the printer name displayed. Select it and click on Next. Finish the wizard. Do these steps on all PCs that you wish to use the printer.
Share Files: You have to create a "share" on the computer that you wish to offer its files to others. Go the properties of a folder, like C:\ for example, and click on the Sharing tab. Click on Share This folder and give it a sharename. That folder, and all folder beneath it, will be shared. On another computer you can find this share by running Explorer, go to My Network Places / Entire Network / Microsoft Windows Network / Workgroup and beneath it you will see any computer that has shares. Expand that computer, and you will see its shares, click on the share and you are connected to the other computer and can access its files.
Generally, share the resource, either printer or folder, you are now a server. Either a fileserver and/or a printserver. Go to another computer, browse your network and connect to the share. You are now a client to the fileserver/printserver. You are now accessing resouces, across the network, on another computer.
Network Usage: All devices share the bandwidth. If two workstations are downloading simultaneously, both get about 50% of the bandwidth. On your home network there is no "dedicated bandwidth" that you can set without getting more expensive equipment, and it is not needed in 99.9% of the time.
If bandwidth is an issue, especially with wireless and Tivo, do wired. Your 802.11g network is not as fast as most people think. The ads say it is 52 mbps, but you will never achieve this speed. If you have two computers with wireless connections in the same room as your wireless router and try to copy a file between them you will only achieve about 13 mbps. This goes for Tivo too. This can be a problem with Tivo if you are copying between them. Wired does not have this speed problem. The only other option is buy much faster 802.11 Pre-N equipment that is now available. But that would cost several hundred dollars to replace your router and wireless cards.
-Rudi