To install Microsoft Web Apps Gallery to your WebSitePanel, you may refer to this article.
1. First of all, get the Web PI(Web Platform Installer).
2. Install it to your server.
3. Open the Web PI from IIS.
4. Find the Web Deployment Tool 1.1 and 2.1 and install it.
With this Web Deployment Tool, it will install the dependencies of SQL Server 2008 R2 Management Objects and SQL Server Native Client.
5. Check if you have MySQL Connector/Net version 6 and above. If not, install it from, http://dev.mysql.com/downloads/connector/net/
6. Now, you may enable the WebSitePanel Microsoft Web App Gallery quota and you could install them from WebSitePanel.