whosamama,
One important point: you shouldn't click into the VCB box to enter you values!
Just as Dylan said, after starting your first endpoint with a ractangle for instance, release the cursor, start typing and hit Enter.
For some European computers however you need to type a semicolon (;) instead of a comma (,) to separate the values. The units are not necessarily needed if you have set them in the template you are using.
To learn more about the correct (and extensive) use of the VCB, see the Usres Guide - especially at the en of each section it tell you tips&tricks about the VCB:
http://download.sketchup.com/sketchuphelp/gsu6_win/gsuwin.html
Have fun (and yes; welcome here, too! )