Making a Custom Magic Items

[Quintain]

I'd like some asistance on creating a custom magic item;

Essentially it is an item that reveals it's powers depending on the level of the character wielding it.

Character Level Power
1st.....................+1 Att Bonus (Untyped)
2nd....................+1 Skill Bonus (Untyped)
3rd.....................+2 AC Bonus (Untyped)
4th.....................+5 Single Class Skill Bonus (Untyped)
5th.....................+2 Att Bonus (Untyped)
6th.....................+1 All Saves (Untyped)
7th+...................TBD

Does anyone know of anything that would assist in creating an item like this (aka one that expands in power as you level)?

 

[Mathias]

Here's an existing thread on the subject: http://forums.wolflair.com/showthread.php?t=9526&highlight=legacy+weapon