Something similar here, MBP 2.2, Leopard 10.5.1 with all updates installed. No funky stuff on this laptop. As I use the laptop on the road I visit many customers having wireless networks. With Tiger everything was just fine. With Leopard problems occur with some WLAN networks.
With one of my customers I am logged into two Ubuntu servers using appletalk and ssh. The wireless connection to those servers never breaks. But within the same network also a Windows DNS server as well as an internet gateway. Very frequently the connections to those two devices break. For instance, if I type
(.1 = gateway, .2 = dns server, .5 = ubuntu box), then I'll see all boxes respond while suddenly the .1 and/or the .2 drops, only to get back after up to 20 minutes (didn't time it as I'm too ****** off by this bug).
Tried to fix the problem with the ifconfig en1 mtu 1492 trick mentioned above. Didn't work. Tried to disable the IPV6, didn't work. Did setup a separate profile for this location with all data entered manually, didn't work. Currently the only solution is to turn off the airport and turn it on again. It looks as if the airport is loosing the MAC addresses or something. This is ******* me off to a great extend as I just cannot work this way and I probably need to downgrade to Tiger or to go back to my Windows laptop.
If Apple would only admit there's a problem here and they're working on a fix, it would help already. But better: have it fixed as my MBP is turning into a joke at this customer: all other systems work flawlessly on the WLAN. There are also a couple of Macs in the house but they're all connected by wire. I don't have an Ethernet connection available and do rely on the WLAN connection - which should just work, didn't I pay Apple for it?