AmrAbdeen

Step 1
Get your Javascript function to add-up the total ready. I have created a simple function which you can customise for your application. You will need to know the ID of the tabular form element you are trying to add.
All editable APEX tabular forms that are ID'ed like f0x_000x. You can find them out by using Firebug (chrome, firefox) or IE Developer Tool by hitting F12 as below.
In my case I need add up the total in Salary column as I add rows or edit entries and add it to the Total Salary text field above the tabular form.
So here is the script. Find out the ID of your field and update the italics part.

STEP 2. Test out the javascript.
Its a good idea to make sure your code works before putting it page attribute.