Compliance is directly proportional to volume and inversely proportional to pressure. So, it essentially describes how volume changes in response to a change in pressure.
Changes in the capacitance of the veins produce changes in unstressed volume. Such as a decrease in venous capacitance decreases unstressed volume and increases stressed volume by shifting blood from the veins to the arteries.
Preload is equivalent to end-diastolic volume. So in the situation you mentioned, where venous return is INCREASED, the end-diastolic volume also INCREASES and stretches the ventricular muscle fibers.
In other words, increased preload is an increase in end-diastolic volume, which is a result of increased venous return (or a decreased venous compliance). The increased preload results in an increased stroke volume (I'm sure you're falimilar with Frank-Starling relationships). This increase in stroke volume is shows on a pressure-volume loop as a increased width of the loop.
An increased afterload would be the ventricle ejecting blood against a higher pressure, which results in a decrease in stroke volume. Since we've already said that increased preload is an INCREASE in stroke volume, we know that the afterload with a decreased venous compliance is DECREASED.
To sum up:
Decreased venous compliance, or more blood returning to the heart:
Preload: Increased
Afterload: Decreased
End-diastolic volume: Increased
Stroke volume: Increased
P-V Loop: Increased width (due to increased preload)