uSE ONE OF THESE TWO GUIDES TO BACKUP YOUR TRILLIAN BEFORE YOU PROVIDE A CLEAN INSTALL:

1.
Backup your Trillian\users\default folder and then a clean isntall should be no problem. 
The users folder stores all of your buddy list information. 
If you want to save the plugins and skins you are using then backup Trillian\skins 
and Trillian\Plugins and of course if you are using sound packs or emoticons 
then backup Trillian\stixe\plugins


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2.
Trillian Backup

It's easy so don't have a heart attack, navigate to: 
"C:\Program Files\Trillian" (or wherever you installed Trillian).

At this point you have 2 choices:

   1. You can zip the entire \Trillian\ folder, which would still be a huge zip file, or...
   2. You can backup your user account settings and maybe your skins.

Using the second option:

    * I suggest making a new folder called "Trillian Backup".
    * After making the new folder, hold down the shift key and click on the 
\users\ and the \skins\ folders and hit "CTRL+C" or right click on the folder and choose copy.
    * After copying the files paste them into the "Trillian Backup" folder 
that you created by either hitting "CTRL+V" or right clicking in the folder and clicking on paste.
    * Now zip the folder with your favorite compression program. (optional)

At this point you are now ready to transfer your files over to your new computer, 
or just save the zip file as a backup.
Before transferring the files to the new computer, install Trillian first, 
then unzip the files to "C:\Program Files\Trillian", then reinstall all your plugins, and you should be fine.

Important note: At this point all your settings have been successfully transferred, 
however your profile may not show up in the welcome screen. This is NOT an error. 
In order to fix this you must click on the "Add" button. After doing so you then must 
name the profile EXACTLY what it was named before. Do this for each profile.