This solution contains two assemblies with the same name, or the SharePoint server already has an assembly with the specified name.

if you prompted for an error "This solution contains two assemblies with the same name, or the SharePoint server already has an assembly with the specified name." at the time of deploying a custom web part or any component in sharepoint as the solution you have to do this :

See if the feature (webpart, lists, etc) that you're trying to add still exists in the "C:\Program Files\Common Files\Microsoft Shared\web server extensions\12\TEMPLATE\FEATURES" path. if its then remove and try to deploy it again.