Hi,
If by pendrive you mean something like a usb device... and if you want it in ext3, then do this.
Find out what device it is. Plug it into your PC then type
# dmesg|tail
You should see something like /dev/sdb1
When you do and you are sure it's the right device, simply format it like this
# mke2fs -j /dev/sdb1
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