You can retain formulas when you add a row but it only works if you add a row before the last row where your formula applies.
You can do what you're wanting with dynamic named ranges.
From reading some of your other responses it seems like you don't want to sum the entire row, maybe because you have the sum listed at the bottom of the dataset or something. With a dynamic named range you can add rows to the bottom of the range, and you also get a nice name to reference it by. It works by using offset and count/counta to deliver a range based on how many occupied cells there are (depending on if you use count or counta).
In my experience you can do an incredible amount of things in Excel before you even break into doing stuff in VBA. You just have to look at any of the numerous resources out there that have tricky formulas available.
You can do what you're wanting with dynamic named ranges.
From reading some of your other responses it seems like you don't want to sum the entire row, maybe because you have the sum listed at the bottom of the dataset or something. With a dynamic named range you can add rows to the bottom of the range, and you also get a nice name to reference it by. It works by using offset and count/counta to deliver a range based on how many occupied cells there are (depending on if you use count or counta).
There are a few ways of doing it listed here: http://www.ozgrid.com/Excel/DynamicRanges.htm
In my experience you can do an incredible amount of things in Excel before you even break into doing stuff in VBA. You just have to look at any of the numerous resources out there that have tricky formulas available.