Here are some helpful utilities for working on EverQuest UIs (User Interfaces).
This isn't a utility but a document released by SOE in 2002 explaining how the "new" UI works. This was the beginning of the system that allowed people to create their own UIs. Note that many things may have changed since then.
ExamDiff is a freeware Windows 95/98/Me/2000/XP/2003/Vista/7/2008 tool for visual file comparison. When SOE patches and changes the UI files, ExamDiff comes in handy to quickly find what they have changed.
Notepad++ is a free source code editor and Notepad replacement.
Paint.NET is free image and photo editing software for PCs that run Windows.
SidlWidl is a SIDL graphical editor, SIDL standing for SUITE Interface Development Language, an xml specification developed by Sony Online Entertainment for their Massively Multiplayer Online Roleplaying Game EverQuest.
The software requires that you have Microsoft's .NET Framework installed. You can download this from Microsoft via windows update or searching Microsoft.com. Most Windows users already have it installed.