There are many e-reading apps that will work on your computer. All the major e-book stores (Amazon, Barnes & Noble, Sony, Kobo, Borders) have their own apps which you can download free from their website.
The Colorado Kid
is no longer free, but possibly you live near a library which lends e-books which has it in their catalogue. You can search Overdrive
for your city/postal code or ask your local librarian.
If there aren't any in your area, then you can use Inkmesh
to search for the lowest price for the e-book version and buy from that store.
One warning if you buy from a store which uses Adobe Digital Editions: when you install ADE to read your books, make absolutely sure to create an Adobe ID when the installer asks. That way you'll be able to transfer your purchased books to another computer or a reader device if you buy one in the future.
Otherwise if you don't register an ID your books will be tied to that computer alone and you'll lose them if it crashes or you have to reinstall the system.
Hope this helps and welcome to MobileRead!