[HELP] How to make a node with sub navigation links and related node links? (URL of snapshot example attached)

In 4.6 the menu on the fly module can do that pretty easily. In 4.7 this is built into the menu functionality.

You can also do this by using blocks and specifying which page(s) that particular block (of subnavigation) should appear on.

Can I use Category Module?

You can.

Unlike vocabularies and taxonomy terms in the core taxonomy module, category module implements both containers (equivalent of vocabs) and categories (taxonomy terms) as nodes. So, you could just create a container called Our Products, create your sub-navigation links as categories and in the body text for both containers and categories, all the text you want to explain them. The posts you tag with those categories (your sub nav block links) will appear beneath this body text on the container and category pages.

However, there is < a href="http://drupal.org/node/63525">an issue with using the menu links generated by the category module as primary links. So, your sub-navigation block will look more like:

Title of block: Navigation
Container name: Our Products
Menu items:
-MS Office XP
-MS Office 2000
-MS Office 97

To get around the current issue of the primary links, you can use a static page for 'Our Products' and put that link in your primary links area. You can then create categories (under Root) for each of your sub navigation menu links, move them into a custom menu block at admin>>menu with the parent set as 'Our Products' (your static page) and enable the block to show on all pages under 'Our Products' in the block visibility settings at administer>>block>>configure

I don't have much of an idea about related links. If you use any of the relationship/relativity modules and if they use taxonomy, you can get them to work along with category module by using the taxonomy wrapper module. I don't know if you will still automatically get the related links block.

If all this sounds like too much hassle, you should keep it simple and follow what the other poster suggested. If you anticipate a lot of content / lots of growth for the site then taxonomy or category will be worth the trouble. If you do decide on taxonomy, though, do yourself a favour and use the category module instead. You will thank me:-)