You can add text to dimension OR place a note next to it. But I would doubt if you can get anything that would pop up like comments in spreadsheet.
Two things too add to the posts above:
1. If you "select" a dimension but do not move your cursor, a little pop-up icon (with a dimension symbol on it) will be displayed. Simply slide your cursor over it and a "Dimension Palette" is displayed. The Dimension Palette provides for a wide variety of common settings and adjustments that can be made to a dimension. The palette lets you add text above, after and/or below the dimension. Some people consider the Dimension Palette a nuisance but I cannot live without it.
2. Another option for annotating dimensions is to turn on the display of Dimension Names, then modify those. The draw back is that "all dimension names" are displayed. This is most useful when documenting multiple configuration but it is a tool just the same.
Just my 2¢,
sorry guys. i wasnt completely clear with what i was wanting. deepak understood and answered my question. the reason i asked the questions is the company i work for wants me to override a dimension on the drawing to something else and the "comment" would tell anyone looking at the drawing in solidworks, that the dimension has been overridden from the correct dimension. also, the comment couldnt be on the printed drawing so not to confuse the shop. this is something i hate doing, but the powers that be saw it as an easier alternative then to explain to the shop why the deminsion was correct without overriding it.
You can add the comment as note . And with SW2015 and above you can set the layer to not to print.