I would probably just go for a PCMCIA card instead of the mini PCI. With a mini PCI you will have to open the laptop case up (could invalidate warranty) and fit it internally. Also, you will pay a lot more for a mini PCI than a PCMCIA card.
The advantage of the PCMCIA card is that you can take it out when not in use to save battery. It is also swappable between laptops in case you get a different laptop later.