This is not the type of job for the faint of heart. There are a lot of things to consider here and you're certainly on the right path by asking what you should do.
As Henry in MI has suggested, the article in The Family Handyman is very good. Your local library may have a copy or even one of your friends. If I'm not mistaken, the issue I'm refering to is as recent as this past Spring. At worst, you can go to The Family Handyman (by Reader's Digest) and call them for a copy. Believe me, the money you spend on the call and on the issue is well worth any money you'd spend on hiring a pro to come in and fix up any mistakes. Not to take anything away from a pro but you may want one to come in and do the rough work, where you can do the finish plumbing and such yourself. Again, this is not as straight forward a job as you'd like.
You have some options. The rest is up to you. My best to ya and hope this helps.
PS. Even if you pay a pro a few $$$ to come in and give you pro advice (but not actually do the work), that would be $$$ well spent. Remember, there are code issues, venting issues, flow issues, tapping issues, 'location' issues, structural issues, etc., etc..