im currently using N-liteos as my quick fix on all of my computers. but wen it comes to fix someone's pcs w/o cd/dvdrom drive, its a very hassle to start over. is there any other way to boot an unattended winXP/WinVista On a flashdisk? is there any other way to mount a bootable iso on my thumb drive?

Yes, it is possible, the method using WINNT.EXE is fully tested and functional, start here:
http://www.msfn.org/board/index.php?showtopic=92644
and follow given links

jaclaz

P.S.: just for the record what you call "fixing a computer" appears to me, according to what you say rather a "re-formatting and re-installing"...