wenbin,You could setup a syslog server on a windows box and run Kiwi syslog to do the logging.Kiwi which is now part of SolarWinds a company that has a bunch of tools for doing monitoring of just about any network device.You could use something like ...

Make sure you are not running a vulnerable version of DD-WRT or you may be compromising the security of the site with the ASA 5510Purchasing an ASA 5505 would be a good solution to help mitigate this risk.  Cisco puts out regular security advisories ...