I've found there is a plugin that searches text files in general. Although it will not show Pegasus' files as e-mails (just as plain text), you can still search them. The plugin is at http://desktop.google.com/plugins/i/indexitall.html?hl=en. Read the text file carefully, because you'll have to indicate during setup which file types you'll want to include - those should be *.CNM (for your main folder) and *.PMM (for all other folders) files, if I recall correctly.
I've found there is a plugin that searches text files in general. Although it will not show Pegasus' files as e-mails (just as plain text), you can still search them. The plugin is at http://desktop.google.com/plugins/i/indexitall.html?hl=en. Read the text file carefully, because you'll have to indicate during setup which file types you'll want to include - those should be *.CNM (for your main folder) and *.PMM (for all other folders) files, if I recall correctly.