Blender 2.49 has for IPO curves something like “Extend Mode > Cyclic Extrapolation”
How can I do this in Blender 2.53 if I want to animate repeated cycle, say, walk cycle, engine rotation, etc.
Use F-Curve modifiers instead. With the animation curve selected, go to the F-Curve editor properties, Add a Cycles modifier and set the start and end to Repeat with Offset. The benefit of the F-Curve modifiers is that you can stack it with other modifiers, and you can add envelopes to change the effect over time.
thank you.