Ans. To list a Web Part with Full Permissions within your Web Application while still retaining a WSS_Minimal permission set for all other Web Parts, You need to create a Custom policy file. This file will be then referenced in SharePoint Web.config file and will allow your specific webpart to be of Full trust.
1. Make a copy of the WSS_Minimal.Config file from the 12\Config folder and paste it into the same folder renaming it to Custom_WSS_Minimal.Config. Now, edit the Custom_WSS_Minimal.Config file using NotePad. Obtain the Public Key Token for the Web Part assembly that you want to deploy, using the following command: sn -Tp filename.dll. Create a new entry in your Custom_WSS_Minimal.Config file for your WebPart. Save the File.
Finally, Create a new TrustLevel element for your config file in the Web.Config called Custom_WSS_Minimal that points to your custom file in the 12\config folder. Recycle the Application Pool and You're Done.