Every time I load KingPin the slider for the texture quality setting is moved to the lowest setting (resulting in horribly muddy textures). All the other setting remain how I left them.
This isn't a huge problem its just a little annoying to have to change this setting every time I load the game.

I have the texture quality setting turned all the way up and it doesn't reset each time I load the game.

You can try to change it manually in some configuration file. Unfortunately I have no Quake engine based game installed atm (unbelievable, innit), so I can't tell you which. But Google is your friend.

I have the exact same problem as the original poster. I've tried playing around with console commands (putting texture appropriate ones into the autoexec.cfg) and making the config.cfg read-only, but nothing seems to help. I still have to manually move the texture detail slider every time after I've launch the game.
My system:-
XP x64, Core 2 Duo E6400, 8800GT 512MB, 4GB RAM, Auzen X-fi Prelude, Gigabyte P965-S3.
I've attached a generated dxdiag.txt, it just has to be renamed to the appropriate file extension.

Did you try setting it read-only in the correct directory ? Because Windows 7 and maybe Vista too, save incompatible program data into a different directory, namely:
C:\Users\**USER NAME**\AppData\Local\VirtualStore\Program Files (x86)\GOG.com\Kingpin\
It's really stupid this is hidden so very well but the VirtualStore is where most incompatible apps store their settings instead of in Program Files.
EDIT: never mind, doesn't seem to work...

I just installed the game and it does the same thing to me too. Is it maybe because the game has naturally low textures and there aren't really any higher resolutions to toggle on?

i had this same problem but i fixed it by going to kingpin.exe properties and activating 'windows xp sp2' compatibility mode and 'run as administrator'
x64 windows7