Treadmill - hurts or harms?

I get inflammation of my SI joints and have a hard time exercising (which I love to do).  The exercise bike hurts my lower back after a few minutes.  The elliptical ultimately hurts my SI joints causing back pain and sometimes full blown shooting pain. 

I just bought a treadmill. The first time I tried it (when it was just assembled and had 15 minutes to spare), my back really ached right afterwards with warnings of shooting pain.  Since then however, I sit with a heating pack on my back for about 15 minutes before hand, then do some stretches (shown in physio), then re-do the stretches afterwards...and my back actually feels better aftewwards. 

I've been doing a very slight incline (like 1-2%) and only 2.7 to 3mph (walking!), but am scared to do anything more as I iknow one wrong move, and I could end up with shooting pain for 2 weeks...and even keepign as I am doing could be the same result.

Just wondering...those with arthritic issues as in this heading, do you find that the treadmill hurts your joints or helps?  And if it helps, any tips (e.g. no incline, incline but walk slower, etc?)

Any advice is appreciated.

Hi i see you are worried about the treadmill have you considered going to a physio they could give you advice and even an excersize regime, as with anything Moderation is the key and a Slow start