PHP form redesign from php4 to php5

I need to redesign the contact form on my site. It is simple contact form to enter name , e-mail and message and send the e-mail to a specified mailbox. Currently my host provider is working on php 4 and the form is working OK. But soon it will be working on php 5 and I know that in the current form it will not work properly. (I guess it is difference in using global variables in php) Only you have to do is to change the code to make it working in php 5.