eBook sell here - How do I create a 'peek inside!' preview for my website?

I've done that a couple of different ways.

In WP, when you create a new post or a new page, you have a tool bar at the top of the area into which you write your content. In that toolbar is a link icon. You can link to a word, a sentence, or an image. Write "Click here to peek inside," and link those words to another page in your site into which you have pasted copy from your book.

Another way is to do exactly what you suggested. Create a book cover image with the words "See Inside" on the graphic. You can place that graphic into a text widget and link it to a page on which you have posted (copied and pasted) content from your book.

To get the code to link that graphic, make a new post (one you will not publish) with just the graphic in the post. Use the link icon to create the link from that image to the WP page containing your sample content. Then while still in the "new post" switch to HTML mode. What you will see is the code you need to use as a link from that image.

Copy that code. Paste it into a new text widget, and your linkable image will show up in the widget area when someone views you WP site.

For folks using HTML this can be real easy. Make a linkable graphic, and have the link send readers to another HTML page with the first page of the book. You can then make additional pages for each of the first 10 or 15 pages of your book, and put a link at the bottom of the page that says, "Next Page." Also put a link to "Previous Page" on each, and a "Return to Home" button.

Hope this helps.

:-Don