Okay, more detailed:
In the CGA admin panel, you have your two items, a book, and a video game. (Well, let's say you have a bunch of books and bunch of video games!)
If you click the "Edit" button to the right of the book you want to 'tag', you can then set a custom 'category' for the book, say "Reading". Then click Submit Changes. Do the same for the game, but set the category to be "Playing".
Then inside of your sidebar, make TWO amazon blocks back to back. Change the titles to match what you want them to show. THEN, we modify the call to show_amazon_items, to something like:
show_amazon_items(1, 'rand', true, "Reading");
For the second call:
show_amazon_items(1, 'rand', true, "Playing");
That'll give you separate blocks. From then on, when you want to change what you are reading or playing, just go into the CGA page and set your new item to "Reading", and then set the old item back to "None".
Okay, now for a little more detail on those calls:
1 == how many items to show. this says show 1. you could have it be 3, and it will show up to 3 items.
'rand' == show up to the above number of items randomly selected from the 'filtered' list. i.e., you could have 5 books categorized as "Reading", and it will randomly show 1 of the 5 on a page refresh...
true == show the image. that's just so people could have longer lists of links without the images.
This is only scratching the surface of what CG-Amazon can do. Including things like showing items off your wishlist (but not tagging them yet when clicking through -- that's an Amazon-side issue), some number of random items matching a keyword, the integration with CG-WhatTunes to show the music your iTunes is playing, integration with CG-Inline to insert a link to ANY amazon product within the body of a post, and more custom queries of the items you've added to the local database.
Post away if you have more questions!