Dave,
I suspect that what imvain2 suggests will sort your problem as there doen't appear to be anything in the style sheet that would have any affect on the search box. However, if you are going to crack CSS, there are some things you could do to make sure that things work.
First - make sure that your xhtml validates.
[Invalid] Markup Validation of http://www.vectorgreen.com/ - W3C Markup Validator
Although as you are using tables, I prefer to leave as 4.01 hml DocType.
As IE6 is not a compliant browser, always best to build in FireFox. As IE7, Safari and Opera are compliant (more or less), they will render ok too. Then all you have to do is tweak for IE6.
AND FINALLY, well you would expect me to say this, ditch the tables and fly without a safety net and build a true CSS site. Eric Meyer's discussion group will give you all the help and support you will ever need.
If you need any help, Dave, let me know via a pm.
Cheers and good luck