Two questions:

1) Gnome 2.6 seems to act rather counter-intuitively: when i click on Home, i get a folder. I click on a folder inside it and instead of changing to that directory within the same windows, a new nautilus window opens. I have many subdirectories, and soon, my whole screen is filled with Nautilus windows! The only way around this is to browse trees by clicking on the root directory and clicking browse directory. Thereafter, Nautilus will behave sanely.

Is there any better solution than this?

2) How do i change the window manager that Gnome uses? I want to use a lighter one to make it go faster.

Thanks

Have you checked in the nautilus settings? It's on the second tab, very easy to find....

Can't help with using a different WM though, why not just use a seperate WM that a WM within GNOME as it will still be a little clunky.

the idea to getting a new window manager running in gnome is to kill of the gnome one first then see if you can get another runing and log out "save the session" and that should do it
try in
gnome-session-properties&
in the second tab put the metacity style value to "Normal" then apply
then do
killall metacity; sleep 1; anotherwm &