It depends on how indepth the auditor wants to go or more correctly what is in scope for the audit.
I would start with the standard port scan looking at standard windows services that are open. You will more than likely find non-standard services open and these are more than likely applications added on top of the OS (Vendor/3rd party apps). These are ripe for fuzzing.
Next use a sniffer (I use wireshark) to look at the traffic in either wired or wireless mode. Look for insecure connections or broadcast advertisements of a devices name and capabilities. If its wired you may need something like this network tap (http://hakshop.myshopify.com/collections/accessory/products/throwing-star-lan-tap-pro) to sniff the traffic.
Next evaluate the system physically. What ports are available and what is required to lock/unlock the device. Some fingerprint scanners can be spoofed. USB/Network/Proprietary ports have their own problems.
Next up take stock of the wireless options. Does it have Wifi/BT/GSM? Does it have anything else like NFC? Each of these protocols have there own attacks. For instance check to see if Wifi does Probe Requests for previous networks it has joined. If so this can give you a list of places the tablet has been (generally bad for executives and such).
Next login to the tablet and perform a standard Windows assessment. After that look for software added specifically for the tablet. Look for ways that battery saving features may be exploited to by pass security.
I would pull any tablet specific software off and run it through a disassembler and look for insecure code, master keys, or insecure network connections.
Since a lot of tablets integrate some sort of cloud service look at what is in place, how it determines what data to sync and use your sniffer to verify it is done securely.
For each of these steps you should look for both built-in or 3rd party mitigations. For instance you can configure MS not to be so chatty on the network.
Depending on how much/little you do you should find a few problems and solutions for them. That would make a nice assessment report while informing the reader the risk level of tablet computing.