As your whole OS is on an 8GB flash card I would be tempted to shut the server down then pop the compact flash into a card reader and take a whole image of the card onto a PC. There are lots of ways to do this just google for raspberry PI SD cloning utils. So once you have a backup then I would stick the card back into the server boot off it and then start with deleting the log files out of /var/log.
This should get you working again. Once the server is up and working then start having a look round for other things to delete.
If things go drastically wrong then restore your image. It would be ideal if you had 2 flash cards so that you could experiment with one.