I was clearing my chat history after seeing a few conversations that could be potentially dangerous to my liberty (i.e. jail) if discovered in my history. While there are methods to recover chat histories, regular clearing will make it harder for any LEO to get evidence in the case (god forbid) you get busted....
So, here's how to clear histories in MSN and Trillian, if you use another chat client and know how to do this, please post up the information or links to a guide...
Trillian Info.
NB - Ensure Trillian is not running while performing this action.
In Trillian, the default log location is: C:\Program Files\Trillian\users\default\logs
Browse to this folder and you will find subdirectories corresponding with each chat network you use (i.e. - "MSN", "ICQ", "AOL", etc etc...).
These will have another 2 folders "Channels" and "Queries", which contain several ".log" and ".xml" file. Each file represents a conversation you have had or messages you have received.
Select all the .log and .xml files in these directories and delete them.