One of my clients would like to incorporate a blog into their existing website and have it still match the style of the page (instead of looking like a wordpress page or something). is this possible to do with an existing blog?
Well, Wordpress is funny that way, it uses a bunch of stuff in the header to trigger functions within the blog.
Really, it's not that hard. Find out what "theme" is being used by the blog (example, twentyten is the one in the latest release, I think.) You'll see that in the WP CP.
In the blog/wp-content/themes directory you will find the theme (in this example, "twentyten." Download this directory and make a backup of it.
Rename this directory something else. Basically treat it as a "new theme."
You will start with three files, header.php, footer.php, and *possibly* style.css. This style sheet you would modify ONLY if it conflicts with your site's styles. Modify it only as a last resort as it contains styles that affect many of the content elements in WordPress.
Open a "template" of your normal site, and open the header.php. Don't mess with any of the "placeholders" or PHP blocks. Add your site's style sheet to the head, and add any containers used by the main site. You'll have to play with it a bit but once you start looking at it you will see what I mean. Repeat for the footer.
Follow the directions on the wordpress site for installing a new theme, so that when you go into the CP you can select your modified theme and make it current.
Of course, if you mess up . . . switch back to the original. :-)