Using shapefile 'Wiki_IED_actor.shp', the input fields for the Getis-Ord Gi* tool (called 'Hot Spot Analysis with Rendering in Arc 9.3) are as follows:

ISAF/ANSF hot spot analysis 
'fr_YY (years '04-'09) = the number of ISAF/ANSF events within a 50k grid cell (according to original data these are 'Friend' initiated events)
'en_YY (years '04-'09) = the number of insurgent events within a 50k grid cell (according to the original released data these are 'Enemy' initiated events)


Supplemental IED analysis (online only)
'found_YY' (years '04-'09) = the number of IEDs found/cleared within a 50k grid cell (According to the original data these are 'IED Found/Cleared' or 'Mine Found/Cleared' category events)
'ex_YY' (years '04-'09) = the number of IED explosions within a 50k grid cell (according to the original data these are 'IED Explosion', 'IED Ambush', or 'Mine explosion' category events) 

Set the distance threshold parameter to 50000 meters (50 kilometers)*


*note that the shapefile must be projected in UTM Zone 41N. The threshold is drawn in the units of the dataframe coordinate system (e.g. decimal degrees in geographic coordinate systems).