This will help you wrap your mind around vBulletins template/style engine:
http://www.vbulletin.com/docs/html/styles_and_templates
Photoshop will work find for your graphics work, most use that or paintshop pro. As for the templates themselves they are just a mix of xhtml/javascript/vBulletin conditionals. Most any editor will work for editing vB templates even notepad, personaly I use
Editplus for such things. Editplus is free to use forever, altho i've bought a copy of it after using it freely for years.
If you just want to change the colors, that can be done without template modification, check out this page:
http://www.vbulletin.com/docs/html/s...nts_colors_etc