I have 3 computers in my home and the first two are close to each other,I want to use the built-in hub of the wireless router to link them up with lan cable.

The third computer is a bit far and I would like to link it with wireless AP. Is it possible for this mixed setup of both wired and wireless?
Also,I want to share one printer with 3 computers.Is it possible for a wireless router setup?

My boardband is 18M, I am looking for either Buffalo or PCi. Which one would you recommend? easy setup,trouble-free,stablized connection and not expensive are under my consideration.

Thanks in advance!

Yes. A wireless router with wired ports can do this. Easily.

As for sharing a printer with other pcs, it's doable, but not without specific hardware or software. Some printers like HP have a network driver for network printing that can be installed on client pcs. The server pc with printer must be on or nothing will be printed. If that's not available, you may have to get a USB printer network adapter. It ain't cheap however. It's called "print server". i.e.

http://support.dlink.com/emulators/dpg310/

Wired is still the easiest way to network. If you need a wireless adapter, go with a PCI one. Unless it's a laptop.

[modem]-[router]-[wired pcs] [wireless pc]