When starting you can pass some options:
java -cp pixflow.jar -mx100m pixflow.Main -o holiday.pfl -p
Directly starts your slideshow holiday.pfl in full screen.
The option -mx100m allows a maximum of 100MB to be used by piXflow. Choose it depending on the memory size of your PC and what other applications you are running. Normaly 75% of your memory is a good idea to start with.