For the first part, check
Tools > Options > Calculation and make sure it is set to automatic
For the second part, you can change the names of tab in code several ways. Each worksheet is a
Sheet object and can be referenced using it's index or it's name. The desired property, as expected, is
Name
Code:
Sheets("Sheet2").Name = "NewName"
As for the "automatically" part, you have to decide what the trigger is and where to put the code.
tc
------> Edit <------
Your formula is set to sum one cell, in a worksheet with brackets in it's name, which Excel 2003 does not allow. Rename your worksheet and try again.