How do I read args passed in address bar?

Folks,

I'm pretty sure it can be done, and I'm doing pretty good with my
javascript so I'm pretty sure I just need a quick point in the right
direction...

If my web page is referenced in the address bar, how can I read these
arguements?

Thus, with

http://www.mydomain.com/mypage.html?abc=123

Is there an easy method to read abc=123 ?

Why?

I want to create a single HTML file that contains a script that will be
used to display an image in the center of the screen. This HTML file
will be used as a popup so when a user clicks on a thumbnail, the larger
image opens... I don't like the idea of having numerous html files
containing reference to each image - I'd prefer to have my parent window
call the popup and pass it arguements, like the filename and size of
the image - One advantage to this method is that I can tailor the size
of the popup window to the size of the image.

Before anybody beats me over the head for using a popup, I
1) am working on an application, not a website
2) my end users will have javascript and popups enabled
3) popups open only with an onClick event occurs on a correctly labeled
link.

All help, via the newsgroup, much appreciated... thanks,
randelld