Re:
I'm not too clear with your question. If you mean a compicated, 'carry any number of weapons but only use 1' kind of system, then you should check out Skating_Cow's Simple Weapon Wielding (downloadable somewhere in the spells section). If you mean that a unit can only carry one weapon at a time, then the concept is fairly simple:
Event
Unit aquires an item
Condition
(item level of (Item being manipulated)) Equal to 1
Actions
set var_item_type = (Item-type of (Item being manipulated))
Item - Remove (Item being manipulated)
If Or, multiple functions
(Item level of (Item carried by (Hero maniplating item) in slot 1)) Equal to 1
(Item level of (Item carried by (Hero maniplating item) in slot 2)) Equal to 1
(Item level of (Item carried by (Hero maniplating item) in slot 3)) Equal to 1
(Item level of (Item carried by (Hero maniplating item) in slot 4)) Equal to 1
(Item level of (Item carried by (Hero maniplating item) in slot 5)) Equal to 1
(Item level of (Item carried by (Hero maniplating item) in slot 6)) Equal to 1
Then - Actions
Item - Create var_item_type at (Position of (Hero manipulating item)
[display a message if you want]
Else - Actions
Trigger - Turn off (This trigger)
Hero - Create var_item_type and give it to (Hero manipulating item)
Trigger - Turn on (This trigger)
This isn't the my best work but it should work. To organize all you need to do is to set the item level of the weapons to one and everything else to level 2. I have read your other threads and, for example, to make this work for sheilds also
-copy this trigger
-make all sheilds item level 2
-replace ever instance of the number 1 to 2 (with the exception of the hero inventory slot)
If this isn't what you're looking for in an answer, please restate your request more clearly.
Cheers