Yep, of course you can.
I find however the best way to edit existing template files is to have the template loaded and then I use firebug to find where i need to edit the CSS to suit my needs.
Also, you can obtain the source file of the template and do your template changes and then change your images accordingly. Then you can do you CSS tweaks after you have loaded the template and again use firebug
Does this help at all?
Are you used to editing dynamically driven sites in dreamweaver?
Because you can download all your template files and open the index.php file in dreamweaver, but of course you don't get a clear look at it as all the image tags are in php and calling different files so its a bit tricky. Thats why I use it online and use firebug
