From the Scripting Manual
procedure ForceWeapon(ID, Primary, Secondary, Ammo: Byte);
ID (Byte): Player ID to change weapon.
Primary (Byte): Weapon Number to set primary weapon to.
Secondary (Byte): Weapon Number to set secondary weapon to.
Ammo (Byte): Ammo to give the player. 0 for default.
This function will force the specified player(ID) to change their Primary and Secondary weapons.
NOTE: Set Ammo to 0 to use the default ammo count for the (Primary) gun.
ForceWeapon(ID, 3, 0, 0);
// Forces player 'ID' to use AK as primary.