PiePanel comes with Tekkit support out of the box, meaning you do not have to ask us to change any server side settings for compatibility.
1) To begin with, you need to head over to the Tekkit website.
2) You then need to download the server files by clicking "Download the Tekkit Server".
3) This will then download a zip, after it has downloaded you will need to unzip it.
4) Get your FTP information from PiePanel and connect, then upload these unzipped files into the minecraft folder. You will need to make sure Tekkit.jar is in minecraft and not any other folder.
5) Head to PiePanel again and go to Settings -> Launch Setings, then choose Tekkit.jar from the binary dropdown and click Change.
6) (Re)start your server and if everything was setup correctly Tekkit will come online.