Creating a timed dialogue box in Windows

I’d like to create a picture that fades after, say, 10 seconds, for my XP or Vista desktop. I have created the image (a reminder to update software), saved it as a jpeg, and put it in my Startup folder, so that it appears on my desktop when I log in. But it stays there.
Is this a matter of a simple VBA script, or would I need an application to do this?
The XP machine has Office 2003, and the Vista has OpenOffice, and Thunderbird as email client, if that’s any help.