OS X+ Non-Apple Router=Madness!

I've been trying to get my friend's wireless router as locked down as possible, but for some reason when I enable MAC address filtering, she can't access the network at all. She's using 2 Apples, an iBook with an Airport card, and an eMac with an Airport Extreme card. The router is a Linksys 802.11b (can't remember the model # offhand).

She's tried the latest patches for both the Apples, and I've tried the newest firmware for the router, but it doesn't seem to have done anything in the area of MAC address filtering. Also, for some reason, the Airport extreme card can't deal with the DHCP, so I've had to configure all the clients on the network manually (no big deal, but mildly annoying).

Does anyone have any ideas why this might be happening? I've had no luck on google, Apple's website, or talking to Linksys techs. I'd really like to add that last lockdown though its already not broadcasting SSID, using 128-bit key, and obviously no DHCP or remote management enabled.

Which version of Linksys is it? There's one version that I've run into that is flaky when it comes to MAC filtering and basically anything remotely associated with secure wireless. That said, I've also found that the manufacturers tend to be rather "card-specific" and don't like "outsiders" (cards with different chipsets) using theirs.

Not broadcasting the SSID isn't really a problem.... The network can still be detected and it is possible that not broadcasting the SSID could have detrimental on the network itself under some circumstances.

Can you alter the MAC address of the Apples to something you want to see if it is reporting one MAC but actually using another?

Hmm, the SSID thing might actually explain another glitch I've noticed lately (I'm on the same network, but wired to good ol' ethernet).

I don't know if you can do that with Macs. My experience with them consists of whatever I've done thus far with her two rotten apples ;)