I've been following a thread regarding this issue from May and thought
I had this solved but not!

Even since I installed IE 8.0 I can't open jpeg attachments in OE6
emails. I am using Windows XP... SP3 I do have spybot running in the
backgrond and have AVG but I have disabled incoming email scans from
AVG.

I tried deleting all the .tmp files, and for a few days opening jpeg
attachments worked. Then it stopped working... So something is
telling me its IE 8 causing this.

Any advise would be greatly appreciated. I can save the jpeg to a
folder and open them from the viewer but that is a real pain in the
neck.