I see there are a few of you struggling with Sketchup. Mostly with dimensioning problems, alignment, etc. Make sure you use groups and components for each major "part" of your model. You can then hide groups you don't currently need, which will prevent you from accidentally snapping to other points in your model.
Also, when ever you are moving or drawing in Sketchup, make sure you lock your axis by pressing one of the arrow keys on your keyboard. This will ensure that you are exactly parallel along a specified axis. Hope that helps.
Check out my top 10 tips every Sketchup modeler should know
. These are the most common mistakes I see people make when using Sketchup.