One really easy way to do this is to create an excel spreadsheet first, with X, Y and Z coordinates for each point. You don't have to do anything special with the spreadsheet, just make the first column X, the second column Y and the third column Z. No headers or anything else is needed. Then, in Inventor, start a new 3D sketch and use Import Points. Then select you excel spreadsheet and you've got center points already located in space. Then simply create a new spline and connect the points. If you have areas of your 3D sketch that need to be a perfectly straight line, skip those areas when creating the spline and go back and fill them in with a line. Then you can apply the smooth constraint to the areas where the spline and line connect to make it tangent. I've used this process for hoses before and it works great and it's really fast. Although, I was given the X,Y,Z coordinates before I started. Good Luck!

Are you using Inventor Professional or Routed Systems for this?

Oh Geez...I'd just install Content Center locally for now. You can worry about the Vault later. It would be a lot easier to use pipe/tube routing.

Find the Routed Systems pdf (not sure of the exact name) on your hard drive and go through that. I also recommend getting a book on Routed Systems http://store.autodesk.com The Routed Systems in Pro make this much much easier. I would forget about Precise Input and creating 3D sketches the hard way.

Even going through the available printed material and Help>Tutorials I have found this area difficult to learn. Classroom instruction with an experienced user is invaluable on this topic. There are a lot of little hidden tricks. I've seen some really good presentations on this topic at AU. Never too early to start working up the cost/benefit analysis to lobby for making the trip.