MacOS – Can I open a folder in the current Finder window, rather than getting a new window for each folder

Personally I use the Open in textmate button that I have added to the toolbar. Steps to download and install the extension are in the link.

Or you can use this apple script

tell application "Finder" to make new file at (the target of the front window) as alias

Open script editor, save as an applescript application to a known location I use /Applications/Scripts and then drag it to the toolbar.

This will create a text file untitled in the current folder.

One (very unrecommended) option would be to assign a shortcut to an AppleScript like this. There's an open bug in 10.7 that makes the script more or less unusable.

tell application "Finder"
    if insertion location as alias is desktop as alias or current view of Finder window 1 is in {icon view, column view} or selection is {} then
        tell application "System Events" to tell process "Finder"
            click menu item "New Folder" of menu 1 of menu bar item "File" of menu bar 1
        end tell
        return
    end if
    tell application "System Events" to key code 124 -- right arrow
    set p to item 1 of (get selection)
    try
        set f to make new folder at p
    on error
        set f to make new folder at container of p
    end try
    set selection to f
end tell
tell application "System Events" to keystroke return