for example i have about 500 lines. in the beginning of each line i want to add a number. so in line 1 i would want \"1)\" and then line 2 i would want \"2)\"
i know
In the more general cases where you want to add a sequence number more selectively (e.g. in the middle of a line, or only for some lines), there are two methods:
Hold down alt and use your mouse to drag a rectangular region, as described in http://sourceforge.net/apps/mediawiki/notepad-plus/index.php?title=Column_Editing Then use Edit -> Column Editor -> Number to Insert as per Tom's answer.
Select a rectangular region again as above, copy the single character # to your clipboard, then use TextFX -> TextFX Edit -> Insert (Clipboard) through lines, as described here: http://sourceforge.net/apps/mediawiki/notepad-plus/index.php?title=Clipboard_Uses#Insert_through_lines_variable_text