To use the old-style contextual menus when you click-and-hold on an applications icon in the Dock i.e. how it worked in 10.5 and earlier, type the following two commands in Terminal dont type the $:
defaults write com.apple.dock show-expose-menus -bool no; killall Dock
All credit for this hint goes to Jeff Johnson of Lap Cat Software, who blogged about the solution. This hint is a significant update to this one, which pointed out you can use Control-click to get the old-style contextual menus. [robg adds: To undo this behavior, you can either change no to yes in the above command, or delete the key entirely with defaults delete com.apple.dock show-expose-menus; killall Dock.]
via 10.6: Display contextual menus on Dock click-and-hold – Mac OS X Hints.