If you are using a native SQL account, you can check in:
There is no date specifically for password changes, but the modify_date does get reset when the password is changed.
SQL DBA,SQL Server MVP('07, '08, '09)
Prosecutor James Blackburn, in closing argument in the "Fatal Vision" murders trial: "If in the future, you should cry a tear, cry one for them [the murder victims]. If in the future, you should say a prayer, say one for them. And if in the future, you should light a candle, light one for them."