Environment variables (%VARIABLE%) are directly accessible in KiXtart, you don't need to pass them in.

In the sample you were given, the KiXtart variable $HOMEDRV is being set to the value of %HOMEDRV% - this is another way of doing it, if somewhat redundant.

Be careful if you are using one of the test / beta releases, as passing variables on the command line was broken in one version.