How to add a separate Attachment column to a Custom list in Sharepoint 2007?
Why you need that?– Juan Pablo Pussacq LabordeMay 11, 2016 at 13:35
OOTB SharePoint Custom List have attachment facility which one can use through ribbon. Also you can add custom button to perform same without using ribbon.
Now if you still want to go with separate column functionality then...
You can use SharePoint Column type "Publishing Hyperlink" and you can directly provide provision to user to upload attachments from SharePoint Itself.
Publishing must be enabled by a site collection administrator for these column types to appear. To enable publishing, go to Settings Small Settings gear that took the place of Site Settings.> Site Settings. Under Site Collection Administration, click Site collection features. Scroll down to SharePoint Server Publishing Infrastructure and click Activate.
For Further Reference:
Now if you require attachments from Computer and not from SharePoint document libraries you can use below reference and add script to modify that functionality