Using WebParts OR Other Solutions Created for SharePoint 2007 in SharePoint 2010

In SharePoint 2010 the 12 hive is now replaced by 14 hive, So we will rewrite and recompile any code that refers to files and resources in “12″ hive. In addition to we must recompile custom code written for Windows SharePoint Services 3.0 and Office SharePoint Server 2007 that does not run on IIS.