How is it broken?
If only the oil has pi**ed out, then it's no problem - you'll just have a very shaky ride, don't go too fast indeed, bike can turn very unstable going through potholes and in the corners.
But if you have something mechanically broken, i.e. the spring, then ride slow as possible. The main problem can be is - you can broke the frame hitting some pot hole or damage the pannier frames etc that can't take huge shock stress.
But i'd say it's doable in both cases. Riding 1000km very slowly with some 30-60kph average, depending on road conditions sounds reasonable (max 2 day trip).
1000kms isn't much to go!
Good luck, RIDE SAFE (on driving slowly, the lunatic drivers can hit you from the back i.e. talking with mobile phone or changing the CD in car audio etc while driving, so be fully concentraded what's happening from the front and back)!
[This message has been edited by Margus (edited 02 April 2006).]