If I'd realised you wanted a classified ads system I wouldn't have suggested the FormMail script from Matt's Scripts in your other post.
Here are some links to classified ad CGI scripts, that are already capable of doing what you want them to do:
And some PHP scripts that do the same job but don't need the jiggerypokery of a cgi-bin:
Obviously you can only use a PHP script if your web host supports PHP.
There should be a FAQ (Frequently Asked Question) page on your web hosts site that will explain how to configure your CGI scripts properly - usually it involves adjusting a couple of lines to reflect your account and then altering file permissions to allow the script to run properly. Most scripts come with a smal text Read Me fle which explains all about file permissions and which lines of the script you should touch, as well as details on what NOT to touch.
Have you checked with your host to make sure that they will allow file uploads ?
Some will and some won't, so it would be worth emailing their tech support and asking them about it, possibly mentioning the name of the script you intend to use and why you want to use it.
The FormMail script I first gave you the link for is fine for processing forms to an email address. It is actually capable of quite a bit more but you need to start tweaking the code yourself which can get a bit hairy if you don't know any Perl/CGI programming. It seems pointless wrestling with it as a script when you can get any one of dozens of alternative scripts that are fully blown classified ads applications.
Check out the links and see where you get.