I hired a sub this year and I would definitely recommend meeting with a tax/payroll professional in your state. There are a ton of things that I wouldn't have known if I hadn't met with someone.
Tom's blog does a good job of explaining the federal stuff that you need to do, but each state and city is different (like in my area, I have to withhold city and school district taxes in addition to state and federal).
http://tomcopelandblog.com/the-many-...ng-an-employee
When I met with a tax guy about this it only took about 30 minutes and he never even billed me for it. If he had, it would have been about $75 based on his quote. Totally worth it.