I dunno about the file server part - maybe you just want to run a cheap PC CPU (without a monitor) all of the time on the network, in which case you could also connect the printers to this computer, set up file and print sharing, and go.

I'd be a little nervous about a print server on a wireless network. Make sure you understand how "secure" WEP is and how to make your network more secure.

Otherwise (ignoring the file/print server solution above)...

Printer: There are several options. If you don't mind leaving one computer on all the time, you can just share the printer among the network. If you don't want to leave a computer on, but the printer can be located close to the internat access point, you could either (a) buy a wireless router that also incorporates a print server or (b) buy a wired print server. If you want to locate the printer somewhere where it's inconvenient to run an ethernet wire, you want a wireless print server.

A wired print server will run you $40-$100 and up (Try tigerdirect.com). A wireless print server is probably $100 and higher -- I got a couple of wireless netgear servers from tigerDirect a year or so ago for $50 each but I think that was a special or closeout (I had to mail in a coupon for the wireless cards for the servers).

Since you're interested in some sort of file server, your wireless gear should all be 802.11g compliant. Bear in mind that having any 802.11b equipment will put your entire wireless network at b speed (11 Mb/sec max vs. 54).