Well a couple of ways you can go about this. If you are trying to open it from a shortcut its a simple matter of changing the properties of the shortcut with the right-mouse button (in the "run" command change it to Maximized).

If this is a link that opens a new window and it starts too small then its a different matter. There are a couple of workarounds but no good answer.

The workaround that works most often involves opening a new window from a hyperlink with the right-click | open new window command. Then resize the window (DO NOT MAXIMIZE, USE THE MOUSE AND RESIZE IT) then do a file | close on that window. Explorer should remember the window size - at least for a while.