To increase the size of the thumbnails in windows XP simply browse to
HKEY_CURRENT_USERSoftware\MicrosoftWindows\CurrentVersion\Explorer
in the registry and then find or create the DWORD values named ThumbnailSize and ThumbnailQuality. Set the thumbnail size to any number between 32 and 256 (decimal), depending on how big a thumb you want; and set the ThumbanilQuality from 32 to 100. Finally restart your computer to see the changes.
