It could be many, many things.

For example:

* You could have gotten some new neighbors that are interfering

* you could be on someone else's point-to-point path, and they are interfering with you (and probably vice versa)

* You may have one or more new users on the network and :

**** They are using 802.11b

**** They are using older drivers

**** They are dumping crap on your network

* Your microwave oven is starting to leak ... the one near your AP(s)

* Everyone also started using Bluetooth (same spectrum, seen as full bandwidth noise to most NICs and APs, though some drivers will coordinate)

* You got a new batch of wireless POTs phones in the 2.4G spectrum

(and on & on, mostly dealing with bad drivers and / or interference)

SO, what to do?

Download netstumbler (www.netstumbler.com), load it on a laptop, and go for a slow stroll. Note the signal strength, signal quality (usually more important than strength), interference, etc

You also want to pay attention to what channels you are using. For 802.11g, stick with channels 1, 6, and / or 11, according to which channels netstumbler says are least congested or interfered with.

Also make sure all of your users are using 802.11g. just one user with 802.11b and the whole network (or the clients associating with the same AP) will slow down considerably.

Also make sure all your users are up to date on their drivers. ESPECIALLY Intel drivers.

If you're working in an "interesting" place, be sure to scan the periphery of your property ... perhaps someone's trying to suck bandwidth or DOS you system.

What kind of security are you inplementing?

Good Luck

Scott