I have Fedora 6 installed in my pc. I can use my pen drive without manually mounting it. But in college, we have redhat ent 3/4 probably where we mount it manually each time we plug our pen drive in. The command we use is
mount /dev/sda1 /mnt/pdrive
Can we do something so that we dont need to mount it each time we plug it in? Can a change in /etc/fstab can do that? If it can, please tell me the command.

Modern distributions are shipping with udev/HAL, which makes automatic mounting of removable devices possible. Early distributions used a hodge-podge of different pieces of software to accomplish the same thing (to varying degrees of success), so it isn't surprising that the older Red Hat version doesn't automount.

To handle automatic mounting on a system that old, you will need to use autofs. autofs isn't exactly user-friendly, you will need to configure and run a daemon for it to work. If that is possible within the confines of your classes/school, then you should be fine.