The previews and sent faxes are .tif files, and presumably for some reason you have associated that file type with Quicktime. I suggest that you find any .tif file on your PC (e.g. where you are storing your sent faxes), right click on one of them, click 'Open with' (not Open), click choose program, select Windows picture and fax viewer, check the box 'always use this program to open this type of file, click OK. Now, when you preview a fax it should open in the picture and fax viewer.
I just installed a fax program (v 5.1) from the windows XP disk and it is sending faxes, but when I push the "preview fax" button, I get the error message: quicktime failed to initialize (error# 2093). After digging around on this site I found that quick time is an apple program, and can cause problems.  My question is, how can I make the fax preview change so it uses another program for viewing? I searched all over the fax program setup,but could not find any info . Any help would be appreciated. Thanks, Guenter   
Windows XP Fax Program 