Hi Mark, also one other note - if you want to get a solid result it's easier to use the the Boolean Difference command to cut your object up rather than using the Trim command.

The Trim command works on the surface skin of objects, while the Boolean commands are oriented towards working on volumes and preserving the output as a volume. So if you take a solid and cut it with a line for example using Boolean difference, pieces of the extruded line will be present in the cut up results sealing off the ends automatically so you won't need to do any additional end capping operations if you do it that way.

See these previous posts for some more description on the difference between Trim and Booleans:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4060.9
http://moi3d.com/forum/index.php?webtag=MOI&msg=3883.3

- Michael