Your best best, if you cannot build your own, is to use a php based form script. BigNoseBird is a good one, and it seems pretty secure.
I totally agree with the comment above. If you have php try phorm jr. If you try to "roll your own" most likely your just become a spammers dream and get your account cancelled.
You can also try our service at http://www.formbuddy.com/ which is remotely hosted. No need to install any scripts in your server