This is controlled in the File Types Tab of the folder options dialog. Open My computer > Click on Tools > Click On Folder Options > Click on the File Types Tab > Scroll down to the .txt entry > Highlight and click Advanced Button.
You should have an action entitled “print”. If not click on new.
In the action box type “print” (without the quotes) and in the “Application used to perform this action:” box type “C:\WINDOWS\system32\NOTEPAD.EXE /p %1″ (again without the quotes)
Tick the Use DDE box and enter “NOTEPAD” under application (Without quotes but capital letters) and “system” under Topic (need i say, without quotes).
Keep clicking on ok until you get back to My Computer, now you can test by finding a txt file and right clicking.
.txt files also have a “printto” option. All setting are the same apart from application, which is C:\WINDOWS\system32\notepad.exe /pt “%1″ “%2″ “%3″ “%4″
Repeat the process for any other file types and you should be set.