I have an old British Army assualt vest that I run in, I put bags of sand in the puches to weight it down.
Like most things, start slowly and build up.
Also bear in mind over here a common reason for a medical discharge from the forces is shin splints and knackered knees; two things to bear in mind if you are overloading yourself and running on hard tarmacced surfaces like pavements/sidewalks.
Out of interest, how long do you run at a weight before increasing?
I started out by putting in 10lbs extra, then another 10lbs two weeks later and so on.
Also, are you doing this for cardio of weights? I can only see a case for it in running and dips/pull ups etc.