Autocad continues to be the industry standard for CAD and Autodesk has done a great job with their 2008 Autocad product. The 2007 version had some hiccups but they seem to have ironed them out with the newest version.
The full version of Autocad 2008 can be downloaded here or you can buy Online at Autodesk directly. After you install it, Autodesk will give you 30 days of the trial version with no restrictions, so take advantage of it.
If after trying AutoCAD 2008 you decide that it is more than you really need, you can always buy AutoCAD LT 2008 from Autodesk! AutoCAD LT is basically AutoCAD without the 3D capabilities and that means the price is much lower. You can also get a trial version of this product so you can compare firsthand for yourself the differences between the two.