Hey YRG! You are definitely on the right track by customizing your WhyPark templates. Even with just a few small tweaks to your templates can mean a significant increase in contextual/affiliate conversions.
Just click on Custom Pages within the admin section next to the domain you wish to add a new page too. If you're adding images and all that jazz you wil have to store those images somewhere online. I use a paid photobucket account for this so I don't burn up bandwidth on my traditionallly hosed sites.
If you're designing a CSS theme for WhyPark simply click on layout and copy and paste your CSS code into the CSS Stylesheet box. The modify your HTML layout below that box as you see fit. Remember to use the tokens WhyPark uses in the HTML layout box and host all images (etc.) within the stylesheet on Photobucket or another image hosting account.
Keep it simple though. Here's a VERY basic customized page I threw up on a brand new domain that specifically promotes WhyPark as an example using site targeting only via Adwords:
WhyPark Domain Name Parking Services