Getting time since.... (PHP)

hey there…
ive got a question in Php i hope someone can help me with…
in a database , along with other info i have a field which registers when the entry was posted, heres an exampel of how the field stores date…
04/10/2005 13:59:59
what i want in php is a script that outputs the seconds since that time and date.

any help greatly appreciated

//VoS