If you're talking about overriding the "Edit" link for a List View on an Object tab - no, you can't override that without creating an entire Visualforce page and overriding the whole tab.
If you're talking about the "Edit" button for an individual record within a List View on an Object tab - no, you can't override that either without creating a VF page and overriding the whole tab.
Would you provide some more detail.
If you're talking about overriding the "Edit" link for a List View on an Object tab - no, you can't override that without creating an entire Visualforce page and overriding the whole tab.
If you're talking about the "Edit" button for an individual record within a List View on an Object tab - no, you can't override that either without creating a VF page and overriding the whole tab.
-Andy
HOWEVER!
If you're looking to override the EDIT page of a record - you CAN do that. Check this link out to override a standard page with a VF page.
http://www.salesforce.com/us/developer/docs/pages/Content/pages_quick_start_tabs.htm
-Andy