This is Acrobat Reader #6 running in Windows 98 SE. It seems to function the same in 2000 Pro or XP.
First you need to download the PDF image of choice.
Unless you disabled it there will be a pop-up from the Acrobat Reader.
after you click the "OK" button, there will be a new task-bar
and a button "Picture Tasks"
Depending on what part of the button you click you either get a drop-down menu or a new frame with the same options.
Just select "Export Pictures"
You will get another pop-up from the Acrobat
Reader . . .
At this point you can change the destination folder from
"C:\My Documents\My Pictures" to where-ever you like and you can also
change the file name from the original name off the website.
After you've decided all the details or just "wanna save the damn thing" click
the "Export" button and you will have saved the image as a jpeg.
About the only down side is that you cannot control the quality of the image,
you will get the maximum resolution that the image was when it was saved as a
PDF-jpeg.
After You've saved the image to your computer you can go to your Display Properties and set the image as a wallpaper.