Hi Siva,
its very easy to mount pendrive in linux if it don't pop up.
login as root on command prompt and execute
"dmesg" command. it will show you that your pendrive is detected as
what type of device.
usually it is getting detected as sda or sdb or sdc or sdd ....
then use following command (i assume that you have a empty directory
in /opt/...
mount -t vfat /dev/sdb1 /opt/usb
hope this helps
cheers