Hey All,
I had an experience while installing a fresh copy of WindowsXP. I forgot to take out the flash and while installing XP it made my USB flash drive unusable because it filled up theUSB flash. Meaning I could not format it because XP would not let it by indicating capacity unkown and it would not let me format the USB flash. Here is what work for me.....

On your desktop: press START/RUN/ then type (diskmgmt.mcs)
You should be able to see the disk(s) on your computer and also the removable disk. Just partition the removable disk and wala the flash has been formated. I almost threw my flash out because it wouldn't work any more.

I hope this helps those who have this problem

Regards
Blakace

this has been addressed many times. But thanks for your contribution.