The file containes cached image previews for thumbnails shown in folders as far as I know. You have to unhide hidden files first. Start>settings>control panel>folder option.
Every folder that you configured to show thumbnails contains this file. The file stays in the folder if you disable thumbnail preview.
TheMajorMMX - Intel P200 MMX @ 225Mhz - V-Tech (PcPartner) Baby-AT mb w/ Intel Triton TX chipset - Nvidia Riva TNT2 M64 w/ 16MB - 256MB M-Tec SDRAM - Still running.....