My son was a 30w preemie, has mild CP and some mild sensory issues, so we have been there
"The Out of Sinc Child" is probably the best reference you will find. Things that I can mention from experience--make sure that your OT is SI certified or at least trained, doing the wrong thing can make SI much worse and even more difficult to fix !! Delayed motor skills can result from being overwhelmed by sensory issues, so it important to address them, but your child has to build up a trusting relationship, so often the OT will tell you what to do and have you do the "tough stuff" for your child.
The biggest treatment that helped us was brushing--Walburger (sp) protocol. Every day every little while and gradually we didn't have to do it any more.
Depending on what your son's difficulties are, there are other things that can help or not. For Jimmy, lots of rough play and bouncing on the bed (I will eventually invest in a trampoline, but...), keeping the TV volume low and reducing background noise in general, having people warn him and ASK PERMISSION before touching him. A box or support under his feet when sitting in a chair. Having his environment organized and clutter free helps him from being overwhelmed. Keepings colors in his surroundings relatively neutral and unstimulating keeps him more calm. Jimmy also has what we call a "large personal space", so we try not to be in the middle of crowds, point out the doors to him (knowing where an exit is helps him feel more in control, even though he doesn't use it, knowing helps) and staying near them until he feel more comfortable. Also, playing with and in large tubs of dry beans or pasta is a good sensory exercise that helps to make touch more tolerable. Playing in trays of shaving cream, whippled cream, pudding, fingerpaints, things like that are also good sensory input.
If you're comfortable with it, let me know what specific issues your son has, and I can try to help more. Also, check out http://www.kid-power.com
It is an organization for parents of kids with mild CP and other disabilities. SI often goes along with CP and other brain injuries. There is really good info on their site, and they also have a discussion list that is excellent. I would really suggest joining, even if just to ask a few questions and then lurk. There is also a SI discussion list run by a friend on the kidpower list, can't think of the address right now, but I can get it if you want.
Please email me if you would feel more comfortable talking that way.
Carrie, Mom to Jimmy 3 1/2