Start IP > Tools menu > select "Restore all Icons" > click "Yes" to verify > click "OK" to apply restore.
After doing that, you can restore the default "Windows XP" theme (after unloading WindowBlinds) via the 'Display Properties\Themes tab\Theme list" and select Windows XP, then click "Apply".
This should restore the majority of the system icons, with the possible exception of ending up with say the ".doc" icon changed from a Word document icon to a WordPad document icon. This type of issue has been there since the release of IP 3.x, and I use the "Folder Options\File Types tab" dialog to restore the Word document icon.
If the above procedure does not work, you can try using the "Repair Icon Images" and "Rebuild Icon Cache" options in the IP Tools menu, again clicking "Yes" to confirm and "OK" to apply the changes.
If these do not work, then your original icon cache was probably corrupted prior to installing IconPackager, or you may have another program which has installed something like an "IconHandler" key in the registry under "HKEY_CLASSES_ROOT\icofile" (normally, you will only have a "Default" key under this key).