Some quick notes. Mostly criticism, but sure it will help you to improve
Simple and neat interface - sure a plus point.
Disadvantages
No client side valdations, atleast not in FF.
Use simple javascript, or try Spry (
http://labs.adobe.com/technologies/spry/ )
Availability of user name - try Ajax, will make it look better - without leaving the page.
When we click submit without proper data or leaving fields empty, it shows message on next screen but no way to navigate back. Give a simple 'Back' link or button.
Put a clock on the question paper page - so people will know the time and do not allow them to submit it once the time is over, or submit it auto once the time is over.
Once we click on an answer radio button, theres no way to correct it, if its done intensionally, its ok, I do not know how the real test works, may be they will not allow corrections ?
When I submitted the test without entering anything (no dropdowns selected) it shows
1. You attempted unauthorized access to a privileged resource.
2. Your inputs contained invalid characters such as '*','|','$', etc.
Suggestion -
1. do not allow them to submit if none of the questions are answered.
2. Give meaningful error messages on server side.
3. Give links (back etc) in the error pages.
LOL, I know how it feels reading these. Reminds me our first debugging session 7 yrs back. We were mad at the guy who was doing validation and debugging ..
Want me to test more ?