It starts just fine because the other DLL that comes with EverQuest Titanium by default simply asks you, "Do you want to upgrade your version of DirectX" and if you already have it installed, it does nothing.
It works like this:

Application loads up, allocates a memory space to the executable. It then imports functions from dynamic link libraries that are assigned to the executable.
When it loads dsetup.dll, in the entry point of said library, it executes more code - some of which writes to eqgame.exe, which in return can load more code when sections of eqgame are accessed. The original library does not do this, it simply exports a function for use that the application can reference.
Once this is done, the application starts, and code is activated as-needed based on what the library has written, for example in the application's main execution thread.

Basically, it's a way of modifying an executable you have no source code for.
If EQEmu had the source code to EverQuest, this DLL would not even be needed.

No. It has never been that small. The dsetup.dll that P99 uses is not the same one that is installed. The Devs have altered it to hunt for cheating programs. And it has been 1954kb since I've been here.

I just joined last night. There is a Trojan in the setup file from p9999.org. I use a program called OMG. It is not free ware.
I also have a problem that may be related to my anti-virus. The dsetup.dll file from p9999 is immediately removed from my EQ directory. the dll file that is on my system is listed as DSETUP.DLL. one in lowercase the other in upper. The file sizes are way different. The DLL that stays in the EQ directory allows me to get to the Character Select Screen but then I get the infamous OUTDATED Files error message. Plus, I get an 0_Unknown_zone error message above the head of a Human Male character. There are no other characters displayed. Trying to just go on into the game leads to a fatal error.
I am using Windows 7. Any help would be greatly appreciated. Sorry if some of this is in the wrong thread, but I originally came looking for info on the Trojan.

I posted a reply asking for help. Thanks all for the help that was already here in current posts. It was my anti-virus and the dsetup.dll file. I told my software to ignore the extracted files directory and the EQ directory. I was then able to keep the p9999 dll file in the EQ file. I can get in the game now. Thanks:))