Need To Take A Step Up In Complexity--please Help

Hi, I've been writing simple database queries for a long time, but I've come to a point where I need to do more work with fewer queries, and I've not been able to make a dent in it. Please excuse my ignorance.

I have a relational database of prices that holds the following info:

Currencies (yen, euro, dollar)
Industries (chemistry, biology, etc)
Company/Institute size (<500, 500-1000, +1000)
Main Products (lab equipment, classroom equipment, etc.)
Series (subproducts) (100ml beaker, chalk, etc)

I want to build a form where my customers can select their currency, their industry and their company size, and then display prices for a specific product (series).

My problem is on the way to the product select. I don't want to display a huge list of EVERYTHING--I want the customer to be able to first select a Main Product, and then populate a list with the relevant sub product for them to select.

However my database is set up with three tables for the individual products: a MainProducts table with main products and ids, a Series table with sub products (we call them series) and ids, and a third table Products that combines the mainproductid with the subproductid to create a unique Productid that is used throughout the rest of the database to get the prices.

(see the relationships here: http://magneticmirror.com/db.gif. The reason for this is that Series in two different MainProducts can have the same name, and so constitute different Products)

The only way I know how to display the name of the relevant series (sub products) is to get the user to:

*select a MainProduct from a list;
*then select all ProductIDs from the the Products table with that MainProductID;
*then for each row from the Products table, take the SeriesID (sub product) and run that against the Series table to get the name of the series corresponding to that ID

if there are 50 series in a product line, that would be 50 individual queries just to populate the list.

There must be a better way. Is this what joining tables is about?

Thanks for any help.

Luud