Yes, you could use one of the Modules and call it whatever you like, and within that module you would identify your different classes.

Hope this helps.

Without knowing what your accounts look like, one option is to make your QuickBooks Classes departments in Sage 50, then assign the departments to the accounts.  

I'm not really sure I understand what you're saying.  Isn't a module a "section" of the software, (i.e. Payroll module, inventory module etc).

I'll give you an example of a typical transaction.  I have a fleet of 10 trucks, 4 belong to Class 1, 3 belong to Class 2 and 3 belong to Class 3.  

I'll use the fuel bill as an example.  That bill has all 10 vehicles listed and the fuel is then expensed to each vehicle, (each vehicle has their own expense account).  When I'm entering the bill, each line has a field that asks for Class -- this is where I would enter either 1, 2 or 3 depending on which division of the business that truck is used in.

Total fuel bill = $$1,000.00

A/C 1000 - Truck 1        $100.00                       Class 1

A/C 2000 - Truck 2        $100.00                       Class 2

A/C 3000 - Truck 3        $400.00                       Class 2

A/C 4000 - Truck 4        $200.00                       Class 1

A/C 5000 - Truck 5        $200.00                       Class 3

You probably want 'Projects' if each truck is tracked separately, or if you ever expect to have more than a few 'classes' to keep track of.

Departments are intended more for keeping track of the separate major functions of a business - for example an auto dealer may have Sales, Parts, and Service as departments.   (or vehicle financing, etc.)

So, fuel for Trucks 1 and 4 can be separate 'service' items that are linked to Department 1, 2 and 3 are linked to department 2, etc.  

In Sage 50, departments work best if each 'department' has separate staff and items that it buys and sells.  If you have a pool of drivers who may operate any of the vehicles, it won't keep labour costs separate