Every now and again when I go to start my jeep ill just get a whirring sound like a drill as if the starter is not turning against anything. It only ever happens when it's cold and I had to try about 5 times before it actually engaged this evening. It's pretty much the same as this guy has: www.youtube.com/watch?v=v35cQ5Gle9A

Time to get a new starter or will it hold out for a while?

It's an 01 2.5td (vm engine)

 

Starters have what's called a 'bendix assembly' . It's connected to the solenoid and kicks the starter gear into the flywheel just before the starter begins to spin. If the bendix is worn or the gears are damaged (starter or flywheel) you'll experience the symtoms you're describing. Check the flywheel teeth for damage before you replace the starter.
It could also be a weak solenoid, but that, and the bendix comes with your new starter.. Go for it