J.,
I too have a newborn and two older children. Here's some advice:
1. Keep the baby in a pack n play, swing or crib - off the floor where "big brother" can climb on her.
2. Have everyone wash hands often - especially your son. if need be, buy some hand sanitizer (there's a new one that's lotion + hand sanitizer in one). Just make sure he rubs it all in and doesn't put it/wet hands in his mouth or touch food.
3. Let him kiss/touch toes - not face, hands or head.
4. What about getting your son his OWN "baby" to take care of? That worked miracles when I had a toddler and infant. The big sister was very busy being a mommy to her baby. I'd suggest a 'plastic bodied baby' NOT a stuffed animal or 'soft' doll. The plastic ones can be washed under the kitchen sink and dry out fast. Plus they can go in the tub, get lotion on them, etc. This really helped our "big sister" to understand "gentle" and that HER baby was HER responsibility, my baby was MY responsibility.
5. I know this is going to sound a bit goofy, but believe me, it works...tell the baby SHE has to wait, be patient, etc. when you are with your son and the baby fusses/cries. Making your son believe that HE is just as important as her is critical. Let him believe that the baby has to "wait her turn" for your attention too.
6. Finally, make it a BIG DEAL to be a big boy, so hopefully you don't have to deal with too much jealousy or regression. If Dad helps him to believe that being a BIG BOY who doesn't need bottles, diapers, etc. will go a long way to get him to ACT like a big boy for you. Especially if Daddy reminds him every morning to be "mommy's helper".
Seems like everyone else answered the "cold" and "jaundice" issues, so I'll just say I agree with them and leave my comments on the big brother stuff.
Let me know if you have other questions...I'm sure I've seen it all.
Sara