the easiest one i found is the one i use - FLED-ids info card editor.
Its simple and easy to use - but you will also need RESHACK at some point. Fleds is in the downloads section - reshack, just do a search of google and it comes up (something like RESHACK editing tool).
Good luck - and Zen has posted a 'how to edit info cards' tutorial - but for weapons its easy as the #4 dll has plenty of room for quiet a few equipment entries (50 or so i think - can't remember off hand) Starts about 320001 i think and goes from there as a hint.....
ids names - 320001
ids info will be 321001 etc
Just add a 1 for subsequent entries - ie 320002, 320003 etc. (Use other entries from weapons and equipment - then edit it and save as YOUR new number - makes it real quick and easy!)