Magento's form system is less than perfect. There are software options that I have found that work really great.
http://www.magentocommerce.com/magento-connect/site-management/crm/webforms-professional-edition.html
Features:
No limitation
Create any number of web-forms and add as many fields to them as you like.
New features
Professional Edition is regularly updated with new features while Community Edition stays at current functionality level.
Stability
All bug fixes and optimizations to the code are first released for Professional Edition.
Contacts notification
Let customers choose who receives their request. Or you can use it as a subject field and assign new requests to responsible departments automatically.
Duplicate forms
Copy complex forms with a single click.
File upload
It lets customers upload files and specify range of allowed file extensions and generates download link in admin backend and e-mail notifications
Image upload
It lets customers upload images and generates thumbnails in admin backend and e-mail notification letters
Results grid filters
You can search results data using grid filters in backend.
Individual e-mail templates
This feature helps you create individual e-mail templates for each web-form
Star rating
Jazzy input field that helps rate anything in fresh and easy way
URL input
URL validation in your form.
Field comments
Text comments under input fields which help customer to submit correct information
Html block field
With this field you can insert html content inside of your web-form.
Date input
Field type with date picker and configurable date formats.
Captcha customization
You can define captcha look and translation for your site view.
Captcha modes
You can turn captcha to always on mode and it will always show up or show it only to unregistered customers.