To enable syslog server do following setp:
logging on
logging host inside x.x.x.x
(x.x.x.x is the ip address of the server)
logging trap [level]
Different levels are as follows:
0 - Emergencies - System unusable messages.
1 - Alerts - Take immediate attention.
2 - Critical - Critical Condition.
3 - Errors - Error messages (this is the default level)
4 - Warnings - Warning messages.
5 - Notifications - Normal but significant condition.
6 - Informational - Informational message.
7 - Debugging - Debug messages and log FTP commands and WWW URLs.
Here is a link which tells in detail about all the syslog messages on PIX-
http://www.cisco.com/univercd/cc/td/doc/product/iaabu/pix/pix_sw/v_63/63syslog/index.htm
If your disk is big enough it is not a big deal for 1 g per day. You only need write a script and delete the old file to save your disk.