Yeah, it pretty much sounds like your filesystem is cooked. If you want to run fsck, first you need to find out which device /tmp resides on. Just type mount and it will show where everything is mounted. It may or may not be on a separate device from /, if you don't see a separate entry for /tmp, then the device is the same as the one used for /. Then, you'll want to boot off a live cd, or installation DVD and go to recovery mode. From there, run fsck -y -C /dev/sda4 or whatever device /tmp resides on. You want to do this off installation media because you do not want to run fsck on a mounted filesystem. So, for hte same reason, do not allow the installation media to attempt to automatically mount your drives (it will usually ask first).
I'd suggest making backups of anything important before you run fsck, because there is always a chance that you'll get some data loss.