I am trying to collect data from my user on an HTML web page in a form. Then I need for that data to post to the SharePoint list once the submit button is selected. The webpage is on the same SharePoint site. I would also like the ability for them to add an attachment if possible.
In MOSS you can customize a list form in InfoPath 2007.. Or create an InfoPath form to submit data to custom list, you can follow this link to get complete knowledge on how you can post data to MOSS List using InfoPath form!
Why I recommend InfoPath form because there you have an attachment control as well and you can bind that control to list item attachments, and here is the usage of Attachment Control