Road Cycling - Road Bike Size ???

I am looking to get in to a road bike and I am 6'1" (33" inseam) tall I just wondered what size bike would be good for me (cm & inches)? Would a bike that is 25" be to big for me?

25" would come out to roughly a 63-64cm bike sounds a bit large to me but I could be WAY off. Check out www.wrenchscience.com they have a fitting guide you can go through. This is not the end all be all of sizing a bike to you but will get you in the ball park.
I'm 5'7" with a 31" inseam and I have 52-53cm road bikes, I have had 54cm in the past just does not feel as good to me personaly though.

.67 mulitplied by your inseam in centimeters. This will pretty much give you proper size.

http://www.competitivecyclist.com/ also has a very complete fit guide. Have someone help you measure when you use it and it should give you a pretty good idea of what you need.

I am 6'3" and was recently professionally fitted for a 60cm Cannondale. Another shop eyeballed me and said 63cm for a Trek. I rode the 60cm and it felt perfect. Since toptube lengths can vary I would recommend getting a pro fit at your LBS.

The proper size will depend upon the specific bike. Especially if you are new to biking, you really need to ride the bike and try it out. You also need to have someone who will apply a critical eye to the bike fit and make sure it is proper for you. It could be the people at the bike shop, although you need to make sure they understand and are not just playing the "well I ride a 56, so you must ride a ...." game. Or it could be a knowledgable friend or someone from a cycling club.

What is the 25" measurement from? Most road-bikes are measured in metric and there are several ways to make the mesurement.