I just noticed this with the startCastStruct:

everquest.h
Code:
struct startCastStruct 
{
/*0000*/ int32_t  slot;                   // ***Placeholder
/*0004*/ uint32_t spellId;                // Spell ID
/*0008*/ int32_t  inventorySlot;          // ***Placeholder
/*0012*/ uint32_t targetId;               // The current selected target
/*0016*/ uint8_t  unknown0018[4];         // ***Placeholder
/*0020*/ uint8_t  unknown0020[16];	  // ***Placeholder (4/7/2009)
/*0036*/
};

Anything else I'm missing?