Take a look at the topic http://simplehomenet.com/forum/viewtopic.php?f=15&t=638#p3286. About half way down page 1 are screen captures for Action AX10B16On that has a Condition that triggers when an X10 On is received from device DX10B16.
A value of 2 in the Condition Attribute Value field represents ON, with an Attribute of Status. An Attribute Value of 3 represents OFF.
For an Effect, the Attribute is Status with a Value of 2 to turn ON X10 and a Value of 3 to turn OFF X10.