right-click on the image and choose "save picture as..." or "save image as..." and save the file to your desktop.
log into msn messenger.
in the messenger window, click 'tools' and navigate to 'change display picture...'. click 'browse' and navigate to the display picture on your desktop. select the display picture. click 'ok'. your new display picture is now ready to use!
download yahoo icon
right-click on the image and choose "save picture as..." or "save image as..." and save the file to your desktop.
log into yahoo instant messenger.
click on the smiley face (or your old display picture) to the left of your username at the top of the buddy list. in the smiley face menu, select on "choose a picture...".
in the "my pictures" window, click on "browse...".
navigate to the location you saved the avatar from avatarstock.com, click on the avatar file so that it is highlighted, and select "open"
make sure your new avatar is selected in the "my pictures" window and click "ok" to set your new avatar. the smiley face next to your picture should have changed to a miniature version of your buddy icon
if you still see a smiley face next to your username, click on the smiley face menu again and select "my display image...". inside this window, click on the radio button labeled "share my picture" and then "ok". your new avatar is now installed!