You can install WordPress from your cPanel using Fantastico De Luxe (Intro to Fantastico). You can find your login details for the cPanel within your welcome email. Please remember to install WordPress into a SUBDIRECTORY such a /blog/, not into the root of your store or you could overwrite your store's files.

Quick Tip: To create a link to your blog from your store, a) make sure you install WordPress into yoursite.com/blog/, b) in your store admin, create a page with the file name "blog.htm" (this is case sensitive), and name the Page Tile anything you want. There is already an automatic redirect in place which will take the user to your WordPress blog when the blog link is clicked.