... or router. IMO the best solution here would be to use a wireless router
Yep, that's what I'd do, and have done. This is a perfect job for a
Linksys WRT 54GL, or anything else that will run
Tomato (very stable). If you really want to get fancy, you can offer multiple (virtual) SSID's with
DD-WRT (much more featured, but installation/future upgrades aren't nearly as stable or seamless). This means you can have a 'guest' SSID (perhaps encrypted, perhaps open, whichever you choose), and another SSID for 'employees' or 'private' (again, encrypted or not) or both, or more, each with different passphrases (or the same), all from one device.
Both of these third-party (and completely free) firmwares are much, much more featured than most stock firmware. You mentioned you are using a Linksys device, I hope it's a model/rev that is supported. If you're not sure, get back to me and I can help you sort it out.
With either Tomato or DD-WRT, you can just disable DHCP and WAN (you can config the WAN port as a switch port, so effectively it becomes a WAP & 5 port switch). If your SME is in server/gateway, just plug the (in this example) Linksys WRT into the LAN port (or anywhere on the LAN, for either SME mode), and tada! Wifi for all (or few!).
Another advantage is that you can mount the WRT wherever you like...typically, the higher the better. So it's not really a big deal (in fact, advised) to mount it on a wall somewhere (preferably main floor/second floor), even 5' - 6' is great (about the length of the power cord), and really helps with range - much more so than if you had a wifi NIC installed in the physical box (which is usually on the floor or in a basement), not to mention the headaches that go with it - extra SME customizing with drivers, routing and such. Bleh.
These become very powerful gadgets when modified, and would suit your scenario very well IMHO. $50 is a steal; the last two or three I ordered were closer to $80.
EDIT: I looked at CoovaChilli and it, too, could easily be integrated to the above config.