wallpaper file type?

No need to upgrade to XP . I believe though on systems prior to XP the only way to show a jpg as a desktop wallpaper is to allow Active Desktop to run. You''ll have to check which is going to use less resources Active Desktop running or using a bmp.
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Thanks, Essencay, for your quick reply . I am not concerned about the files sizes for myself. If I wanted to upload my walls here for others to use, would it matter whether they were bmps or jpgs? I have d/l some wallpapers which I found were jpgs after the fact and cannot use them due to the Active Desktop requirement. I'm just wondering which is the best format to u/l. Thanks!

jpg for upload, but you could just leave them as bmp on your machine, as Essencay said.

Wallpaper changer programs will allow pre-XP system to use jpg, without using Active Desktop. I always used jpg files when I was running 98, and W2k. 

Irfan View will set the jpg as wallpaper - and it's free

Forgot about IrfanView....great little proggie

Thanks for the tips

I looked at the IrfanView help file and what it's actually doing is converting the non-bmp wallpaper image into a bmp.

"IrfanView will save a BMP file called IrfanView_Wallpaper.bmp in your user settings folder (Documents and settings\User\Application data\IrfanView\) and set it as wallpaper."

File conversion seems to be my answer.