Downlaod the .141 OS from AT&T that's in the stickied thread at the top of this forum (the actual working link is on the second page of that thread). Install it to your PC and run Desktop Software 6, then click on Applications. Scroll down the list of apps that eventually comes up, and you will see Twitter. Click on the plus sign next to it to bring up "Pending Install" and then click on Apply.
The version of Twiiter in App World (an earlier version) doesn't integrate into Social Feeds on the Torch.
It is a good idea to do the above but I would just go to the mobile website while on the mobile network and install it. You will have device identity issues causing an error that reads something like "sorry your device does not meet the minimum requirements" if using WiFi.
Posted from my CrackBerry at wapforums.crackberry.com