You already have it and it does basic tables which are good enough for simple two-column scripts. Apple even has a knowledge base document on it here (at the bottom).
To create a table, from the Format menu, choose Text, then Table. In the resulting Table window, enter the number of rows and columns you want, select the text alignment, choose the cell border thickness and color, and choose a background color. Your TextEdit document updates as you make changes.
If you want to use Pages there are some tips on two-column format in a previous post of mine here.