A Hip Tip on Converting a Surface to a Solid...

You can turn a surface into a solid fairly easily in AutoCAD 2007 (something that was not nearly so easy in previous releases).  The new THICKEN command is one of my favorite command Newbies.  Simply select a surface and input the thickness and poof - it's now a solid! 

Command:  THICKEN
Select surfaces to thicken: Select one or more surfaces to thicken into solids
Specify thickness <default>: Specify a thickness value

The DELOBJ system variable controls whether or not the original surface is deleted in the process.  Imagine using the new LOFT tool to create an awesome surface - and then using THICKEN to turn it into a solid...Very handy tool!