if you are refering to the image resizer powertoy, just reinstall it, that
should fix the problem.
http://download.microsoft.com/download/whistler/Install/2/WXP/EN-US/ImageResizerPowertoySetup.exe
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BUT, try this first: from a command line enter this command:
regsvr32 shimgvw.dll
that should re-registry the XP Picture and Fax Viewer, which is necessary
for the resizer to work. Many (older) tweaks recommend disabling this
default viewer, and folks just go ahead and do it. If you have SP1, this
viewer is not as obnoxious as it was, you don't need to disable it
anymore. if after re-registering it you find that clicking on a jpg opens
the viewer instead of your preferred tool (irfanview I hope), just go into
your tool and have it reclaim jpg's as its own (options menu, file
extensions).