I'm not sure I can help you, I'm posting mostly out of sympathy.
Typically, there should be something wrong with the install, when it aborts like this. Like something doesn't point right and some stuff can't be found, so the game has no other option than exit.
First the selfevident: (from readme)
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Game Fails to Run after Restarting an Incomplete Setup
If you interrupt Setup while it is installing files, then return to the Setup menu and rerun Setup again to completion, Dungeon Siege may not start. To resolve this issue, exit Setup completely and rerun Setup from the beginning.
Game Fails to Run after Second Install
If you reinstall on top of a new installation, the executable file may be corrupted and will prevent Dungeon Siege from starting. To resolve this issue, copy your saved game files to a safe location and uninstall Dungeon Siege, restart the computer, and then reinstall Dungeon Siege.
Microsoft Games SafeDisc for Windows XP
When running a restricted user account with fast user switching under Windows XP, some games will not start correctly. The game requests that the original disk be placed in the drive, even if it is already present. To resolve this issue, download and run the file at
http://www.microsoft.com/downl...se.asp?ReleaseID=35831.
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Otherwise, this problem at launch could also be something related to the CD-copy protection.
Wildly guessing, try getting rid of things like CD-RW UDF device and maybe antivirus too.
It really shouldn't be any thing like this, but.... (and I did have some problems with 'InCD', and eventually chose to uninstall it.)
