You never know where the IT guy is really coming from. I always assume that they are either incompetent, defensive about their turf and/or simply operate in passive-aggression mode. Then I hope to be pleasantly surprised.
In addition to the tech specs, we also always specify in the SOW which rights we will need on which machines and networks. We also balk at doing work on the Domain Controller, simply because it can raise further security concerns, or worse, claims that we damaged their systems. In our proposals/SOW for firms that have known problematic IT people, we add a clause stating that if we are forced to reschedule work because we cannot gain usable access that we charge an extra $$ fee. (And then the first time we have the problem we call our buyer and remind him/her of the clause, offering to waive it this one time if the problems go away. They always have.)
Wayne is right: if you have trouble with the IT resource, your buyer has heard it before and is likely to be helpful. Working through him/her is usually a key part of smoothing the waters.