This code works for flexible window widths, but the images need to be fairly small; if the total of their widths is more than a small window that they are inside, one of them will go down below the others.
<div style="width: 100%; text-align: center; background-color:
#eeeeee;">
<img style="float: left;" src="image1.jpg" alt="image left">
<img style="float: right;" src="image2.jpg" alt="image right">
<img src="image3.jpg" alt="middle image">
</div>
The side divs operate a float but the center image (coded after the other two) operates the text-align: center in the containing div and moves up into the space between them (if there is enough room).
Tested in IE7 and Firefox.
If you want all three fixed to the bottom of the window regardless of the window size. edit the containing div to:-
<div style="width: 100%; text-align: center; background-color:
#eeeeee; position: fixed; bottom: 0; left: 0;">
but it won't be fixed in IE6 which doesn't support position: fixed and you may find that it covers other content above (the background-color will cover other content) so you may need to add a margin-bottom to whatever div is above to provide a bit of space for the fixed images.
Code downloaded to my PC will be deleted in due course.
WIN7; IE9, Firefox, Opera, Chrome and Safari for Windows; screen resolution usually 1366*768.
Also IE6 on W98 with 800*600 and IE8 on Vista 1440*900.