James,

Thanks for the reply.  I've ordered "Agile Web Development with Rails:
A Pragmatic Guide", but couldn't wait to get started in the framework.

For the example I gave, where would you store the unique attributes
associated with my subclasses?  For example where would the
"TowingCapacity" field be located?

In my application each of the 10 subclass has around 20 unique
attributes.  I hope that the solution won't require me to create one
table with over 200 fields (with each row having 180 NULL fields for
the non-applicable attributes).

Thanks!