I had the same problem when I started with openHAB, I ended up doing it like this.
Item
Switch networkLamp "Lamp"
Sitemap
Switch item=networkLamp
Rule
rule "Network Lamp ON"
when
Item networkLamp received update ON
then
sendHttpGetRequest("http://192.168.1.3:6001/do.nes?arguments=100")
end
rule "Network Lamp OFF"
when
Item networkLamp received update OFF
then
sendHttpGetRequest("http://192.168.1.3:6001/do.nes?arguments=0")
end