This guide will explain to you how to run Torchlight in wine under Ubuntu 9.10.
First, you must start a terminal. Next, install wine and do a little customization:
sudo apt-get install wine
wget http://www.kegel.com/wine/winetricks
sh winetricks vcrun2008 directx9
wine /the/path/to/the/torchlight_installer.exe
Now run winecfg, and click on Graphics->Emulate a virtual desktop to let wine emulate a desktop in a window, otherwise torchlight won’t run.
Finally to run the game, type this in the terminal:
wine ~/.wine/drive_c/Program\ Files/Runic\ Games/Torchlight/Torchlight.exe SAFEMODE=1
This is the method that worked for me, so I hope it works for you to. 
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Hey !
I did exactly what you did.
But my game does not launch, it only opens an emulated desktop and then closes.
Could you try to help me please ?
Hi Felix.
According to the Torchlight entry in wine’s appdb, only versions of the game bought from Gamersgate.com or Steam will run correctly. Did you buy the game from one of these two retailers?
Maybe it’s a problem with the drivers for your graphics card, but I’m not sure how much that would matter. Do wine output any errors?