Did you connect the laptop prior to connecting the Linksys? If you did, my guess would be that the newer equipment may be 'smart' and over the 'life' of your paid internet period may only permit one MAC address to inhibit fraud. I've never had a problem at any hotel with my Dlink DWL-G730AP and I've never changed the MAC. I simply plug it in and go, it works flawlessly.

Failing that, I'm not really sure. I don't think it'd be a MAC filtering issue. Linksys makes lots of products including PCMCIA WiFi cards that would use similar MAC addresses.