All Right, Another Question on my favorite Xmldialog

I would make a simil-talk comand to say to the npc to Arm/Disarm his-self (that word exist?)
i have made:
Command: Disarm Yourself!
Text:*Drop Out his weapon*
Condiction: isn't important now i think...
Action:SETONTHIS/UNEQUIP,Firstvalid,false
And It work...
Now i would make the Arm Trigger...
Command:Arm Yourself!
Text:*Bla bla bla*
Condiction:The weapon is on his backpack
Action:SETONTHIS/EQUIP/The weapon in his backpack
How i can specify to the Npc "That damned weapon (One then using yous best combat) on your Backpack!"?
Tnx for any Help