This how-to explains how to brand your installation of Spark IM client with your company name and logo along with some other bits and bobs
Install Spark
Make sure that the latest version of Spark is installed on either a test machine or a single client machine that you will use to modify the install.
Find the file to edit
The next step is to find the file that you need to edit to brand spark. The following steps assume that you have installed Spark in the default directory...
Navigate to C:\Program Files\Spark\lib
Find the file 'spark.jar' and open it with WinRar (other archivers will work but WinRar tends to give best results)
NOTE: Open the .jar file, do NOT extract it.