Here are a few suggestions that I have.
First of all I'm assuming that you tried to make this use the colors of vBulletin 3. If not, sorry, ignore any references to vB3 that I make.
- Some things have a vB4 blue look and not a vB3 purple look, for example the bar above posts that contains the post date+time.
- The advanced search link in white is not visible
- The navbar links (new posts, private messages, faq, calendar, etc.) should be a slightly darker color to be more visible
- Big Blue Buttons (Reply to Thread, etc.) should use the vB3 purple color
- Links in the (Thread Tools, Administrative, Search Thread etc.) bar should be much lighter to be more visible.
- The head of threads table (forumdisplay, contains title/thread starter, replies/views, etc. ) is using a vB4 blue color and not a vb3 purple color.
Other than that thanks and a nice idea, I will probably offer this to my members since a lot of them like the vB3 default skin.