Additional Note:
The Setup with manuall copying of vc8 runtime works completely on 2000 (incl. JPEG Support). Only on XP JPEG Support fails.

Probably qjpeg depends on some other library (like libjpeg or simmilar) which is not available on the target system. Use a dependency walker to check that out.
Dependancy shows no missing libraries. Copying alle dependacies into app or imageformats folder makes no enhancement.

c.