My bro uses his Sony Vaio and my GF uses a Dell laptop. They bth have onboard Wrieless cards and have no problems.
Ive just checked The Netgear wireless utility on my work HP laptop and the transmit/recieve performance meter reads around 1% !!!
....Arrrrrgh
Might pay you a visit Soopah to check this mini PCI theory of yours out!
Real pain with this is that its not even my laptop!!!!!!