<Where> <Eq> <FieldRef Name='dateTimeField' /> <Value Type='DateTime'> 2008-03-24T12:00:00Z </Value> </Eq></Were>
add in the IncludeTimeValue='TRUE' property to the Value type. (like below)
<Where> <Eq> <FieldRef Name='dateTimeField' /> <Value Type='DateTime' IncludeTimeValue='TRUE'> 2008-03-24T12:00:00Z </Value> </Eq></Where>