I mentioned about PDF preview handlers in a previous post.
Here is a picture showing how an AutoLISP file with the LSP file extension is previewed in Outlok 2007.
Here is a preview in Vista Explorer.
The above was achieved without any extra coding. A simple registry hack made lsp files and other files to be handled just like plain txt files.
Here is a sample reg file including some txt format files that are used by AutoCAD. CUS, DCL, LIN, LSP, MNL, MNS, MNU, PAT, PGP, SCR and SHP. This works for Windows Vista and Microsoft Outlook 2007. If you want other files to be handled like TXT files it is simple to edit the reg file and add or remove these. For example you might want to add CMD, BAT, VBS.
Here is a snippet from the file.
To remove it you can create a REG file with lines like this.