1. Download and install FireFox (if you don't have it already)
2. Install Firebug (an add on for FireFox)
3. Go to your site in FireFox, under Tools, start Firebug and Viola!
you can play with your css to your hearts content. In Firebug, you can select your css, then select the element you want to change, and edit. Changes will be shown in real time without actually modifing the css, so you can see if your changes give you the desired effect. Once satisfied, go to your real stylesheet and comit the changes.
Even I can do a little bit of this, so that means most anyone can as well.
You can find FireFox and Firebug here.
www.mozilla.com/firefox
Good Luck