check the faq:
viewtopic.php?f=45&t=4098&p=56993#p569911. purge all hands and import them after u reinstalled
2. backup database using PGAdmin III
3. backing up a postgres database from the command line
If u keep the structur of your harddisks u could maybe just copy the whole database to a different harddisk, reinstall everything and replace the postgres-folder with the one u copied earlier - but no promise - try one of the above options - its safer