Creating an angled workplane in Inventor, version 10 at least, is actually very easy.
In the image I've posted below, I created an extruded block. To create the angled workplane, I first selected a face, the 'top' and then one of the edges. Inventor then prompted me to enter the relative angle of the proposed workplane. I arbitrarily used 32 degrees.
I the created a sketch on the workplane, and placed a point center by eye. Then, using the hole command, I placed a plain hole through the part using the 'through all' terminator.
I eyeballed the placement of this hole. You could constrain the placement relative to other geometry a few ways though. The nice thing about this, and any method that uses a feature, over using a boolean subtraction, as Al suggested he might do in AutoCAD, is that this feature remains adaptive and can be later changed. Changing a solid model in AutoCAD is just a pain in comparison.
You could also form a hole that follows a work axis between two workpoints, although getting a fully formed hole is a little tricky. I can go off on that if someone wants me to, but I am guessing that the angled workplane is probably adequate for what the OP was looking for.
