clock in datagrid

Hi,
i've a requirement to have a timer in my datagrid row.when a user is working on one row.he has to click on say a start button & the timer will start.until he finishes the work,ie stops the time.next time when he'l start working on the same row,the timer value has to start incrementing from the latest value.(which will be the last time's timer value)Also he can at the same time work on multiple rows,clicking on start buttons,row wise which will be running for each row & calculating the time untill stoped.
plz help me if it can be done in some way,its quite urgent & revert me back to my personal Id: DotNet_Pr@rediffmail.com
Thanks in advance