BACKGROUND INFO
I have a .DV-AVI file that I exported from Windows Movie Maker. I
opened it in Quicktime Pro and am converting it (exporting it) to a
.MOV file.
Hopefully, this will expand the number of users who can watch the
video clip online.
I heard that .mov is the file extension for Quicktime for PCs and .qt
is the file extension for Quicktime for MACs.

THE QUESTION
Since I am creating the Quicktime file on a PC, I will get a .mov
file. Will MAC users be able to play back this .mov file a using the
Quicktime player? or is it just a PC that can read this type of file?

Assuming you're not using any unusual codecs, it should play on any
computer that has a Quicktime player.

Also, if your main aim is to make it more accessible to people across
platforms, you might want to consider converting the video to a Flash
.flv or .swf file.

FFMPEG (http://ffmpeg.sourceforge.net/index.php) can convert between
many file formats and is free, aside from that, there are other
dedicated file conversion programs that convert from eg: AVI directly
to FLV with a SWF wrapper for use in a webpage, like
http://www.flash-video-mx.com/

QuickTime's .mov codec is cross compatible; if anything, Mac users
find if preferable to anything encoded as Windows Media (Ever since
Microsoft stopped supporting Windows Media Player, it's harder and
harder to convert it to something Mac users can view).

The format compatibility goes something like this-

.mov - Best on Mac, good on Windows
.wmv - Best on PC, passable on Mac, except Windows Media player 10
files, which do not work.
.avi - Cross compatible, but requires a variety of software to run
properly, like DivX and Xvid.
.mpg - Cross compatible, but very inefficient file-size-to-quality
compared to the other formats.
.mp4 - MPEG-4 encoded video, seen most recently in the iTunes Music
Store's video section. Cross compatible, although better on the Mac
side.
.dv - The standard for digital video, and very high quality, but huge
file sizes make it inefficent for the web.

They certainly will be able to open the file and view the video.
There's no doubt of it!