A half note is still two beats.

A dotted half note is half as long again, so would be three beats.

The duration of the notes remains constant regardless of the time signature.

What often causes confusion is using the US names for the notes. I'm a Brit and learnt to read music in school using entirely different names for them. I think the worst example has to be "there are three quarter notes in one bar in 3/4 time signature"..... Use of the US names for notes is becoming pretty standard, though.