I used a really nice and affordable nice softwre for some years now, Xplorer2 (http://www.zabkat.com), with multi tabs, scripts, quick view, sync, editable search and many more options (for the explorer replacement part) and unfortunately only on my xp box because it doesn't seem to work on 7, a really nice software also called Direct folders (at codesector.com), allowing you to jump to any folder/disk with a double clic on empty space in save/open dialogs, with the ability to set favorites jumps (on the fly or by options).

EDIT : Direct folders does work on 7ven, at least with keys combination (looking at codesector, the compatibility with firefox 3.6 is an issue but couldn't say more as I stayed with 3.5.8 to keep it working). Maybe some tester could try firefox 3.6+ and direct folders with keys combination....