Can vinyl siding be painted or stained, and more importantly, does it last or will I be repainting every year like a wood sided house?
Yes, you can paint it. Make sure you clean it very well (use a TSP Cleaner) and then use a primer first (although some sites say you can get away without a primer).
Also make sure to paint it a lighter color than the current one:
I assume you're painting with a lighter color paint - vinyl siding painted a dark color can have problems with warping and expansion in direct sun.
The expected life of the paint job will be dependent on the weather conditions for that area of the house and probably be about the same as a wood sided area.