On Mac OS 10.1 ... lost preview.html.
All downloaded files are coming in as Colorsync...

Instructions to restore Preview.app
download pacifist
http://pacifist.en.softonic.com/mac
Install pacifist
Drag pacifist to applications folder and open.
When you open it read the instructions,
insert Mac OS X Install CD 1
then click the button 'Open Apple Install Discs'
A list will pop up and if it shows your mac install disc in the list click 'Choose'
Then let it load, you may need to insert disc 2 as well, then disc 1 again.
When the next window opens follow these instructions

Click on 'Contents of OSInstall.mpkg'
Click on 'contents of essential system software'
Click on 'Contents of essential system software group'
Click on 'Contents of Essentials.pkg'
Click on 'Applications'
Click on 'Preview.app'
And finally click on the 'Install button on the top left of the window, big yellow arrow looking thing.