I have a USB pen drive that I use quite a lot, but I can only mount, unmount & write to it as root.

I mount & unmount from the command line like this:

mount -t msdos /dev/sda1 /mnt/usbhd -o fat=32

(I use it with windows machines too)

Are there other options I can use so that users other than root can mount and/or write to it?

I had an entry in my /etc/fstab but took it out because the machine wasn't happy if the drive wasn't in place when it shut down.

Have you tried to give write permission to everyone? chmod a+w /dev/sda1 ? I am not sure if this will allow you to mount it as well... but I am pretty sure it will allow everyone to write to it.

Not sure if this will work, but when moutning, try give the option

-o umask=000

Taking a stab in the dark here though, read through the umask man page to see what I'm on about.

Cheers.

Your mount command is wrong. You should use
mount -t vfat -o sync,users,umask=000 /dev/sda1 /mnt/usbhd

The umask will let any user write to the drive. sync will make sure the data is writen to the medium instead writing to memory. users lets all users un-mount the medium. vfat is fat32.

If you want LINUX to automatically mount your USB medium you have to use hotplug and tweak the script. hotplug is just a bash script to detect USB devices and mount them to your wishes. I suggest you do not add an entry fstab for USB devices because LINUX names each USB device and it will not be the same every time you insert a USB device. Sometimes you may put a USB hard drive first and it will work how you want it when you add the pen drive.

If you want to put an entry in your fstab and forget how it looks in the /mnt directory.
/dev/sda1 /mnt/usbhd users,noauto,sync,umask=000 0 0

Then all you need to do when you insert the USB pen drive, type mount /mnt/usbhd to mount it and umount /mnt/usbhd to un-mount it.