Depends where you installed Photoshop, but should be something like the following:

C:\Program Files\Photoshop 10.0\Adobe Photoshop CS3\Plug-Ins\Extensions\Bigger Tiles

(Expand your search with wildcards: eg "*bigger tiles*" or reduce the specificity further such as *big* to have a better chance of returning results...)

The plugin itself is named "~Bigger Tiles.8BX" & you have to remove the '~' & restart PS for it to take effect. (ie installed as OFF by default)