There are several threads about this already posted.

The main issue is that the driver for inbuild wifi does not support packet injection, which makes even wep attacks a slow affair.

There are a couple of ways around this - there is an open source driver in development, which may support injection at some point (even now perhaps, I didn't look).

The other way to go about this is to use an external usb nic. There are drivers available for r73 and rtl8187 chipsets, but others could be compiled if they are available for linux (which is most things).

The tablets don't enough juice to power an external nic, so you would need a powered hub, or some other way to power the usb stick (I used a "three-leg" usb cable like you get with usb external
drives and a battery pack).

WPA attacks are all about computation time and/or rainbow table storage, so the tablets aren't really suitable for that. Better to use the tablet to gather the iv information then go back to a PC to do the crack.

The idea of using a tablet for this type of work sounds glamorous, but the execution isn't. It is fiddly and time consuming. And if you are demonstrating to a customer, having all the wires and bits and pieces often dilutes the message that they need to fix their security. They see all this "specialist" equipment and figure only a small number of people could accomplish it.

Better to use a laptop and sit somewhere comfortable, and even show the customer the process (if wep) so they can see how quick/easy it is.

Or better still, speak with confidence, explain WEP is rubbish, and just tell them they need to change without all the bother of a demo.