As was mentioned, the CAD/CAM package you use depends on what you plan on making. (and your budget)
My recommendation is do not spend ANY money until you understand the process. You can easily use free software to design parts and run your machine.
A lot of parts can easily be made without making a 3D model of them. And most CAM software that works with 3D models is rather expensive. An alternative is to do 2D drawings, save as .dxf files and convert the .dxf's to g-code. You can simply draw the profile of the part, and basically the router will follow the lines in your drawing. You might want to look at ProgeCAD, at
http://www.progecad.com/ If you choose to use Mach3 to control your machine, it comes with a simple CAM program, called LazyCAM. It's currently being reworked to make it more user friendly and add more power. Another free converter is ACE Converter, available at
www.dakeng.com If you need more power and control, you can step up to SheetCAM at ww.sheetcam.com You may find that an inexpensive or free 2D CAD program and one of these options will allow you to make anything you may want to make. If you find you really do need 3D CAD CAM, expect to spend quite a bit more money.
I'd recommend that you download Mach3, watch the videos at
www.machsupport.com and install it and learn to use it. Get ahold of a cheap or free CAD program, and learn how to convert .dxf files into g-code using LazyCAM, and simulate the g-code with Mach3. Mach3 is free for up to 1000 lines of g-code, which will let you do quite a bit of experimenting and learning. As you learn more about the whole process, you'll be in a much better position when the time comes to spend your money to make an educated choice.
As for TurbocADCAM, I checked their website, and they don't have it listed anymore. It appears to have been replaced with a 2.5D CAM plugin for TurboCAD for $299