okay let's see if I can help you out here a little
Are you using MySQL? Oracle? can you please share that with me?
ALSO what are the fields that you are trying to populate in salesforce, are they custom or are they already defined
Sorry for all the questions sir, but it will help me define what it would take to help you get a script up and running to populate the Salesforce leads object from your database.
Can you look at my profile and see if you may contact me on one of my IM's or Skype
also have you thought of using a web to lead to populate your salesforce leads tables >
Fight Web to Lead Spam w/ Akismet | Perspectives on Salesforce.com
Anyway get back to me and I hope this helps
~Mike