Have you tried linux-backports-modules-karmic? I believe I have the same Philips adapter(It's atleast a Philips adapter) on my T41p and it works pretty well with ath5k. Same result with my T60 which had horrible connectivity using ath5k until I installed the backport package.
Before I installed linux-backports-modules-karmic I used ath_pci on both laptops.
@Jarmo
Have you tried linux-backports -modules- karmic? I believe I have the same Philips adapter(It's atleast a Philips adapter) on my T41p and it works pretty well with ath5k. Same result with my T60 which had horrible connectivity using ath5k until I installed the backport package. -modules- karmic I used ath_pci on both laptops.
Before I installed linux-backports