If you're using a Magento 1.3 theme with a Magento 1.4 install your contact form will not work.
It just shows an error
Unable to submit your request. Please, try again later
Add the following line to the form.phtml The location of the file will depend on wich theme are you using (base, blank...).
Add this after the <form> tag:
<input type="text" name="hideit" id="hideit" value="" style="display:none !important;" />