You should have three sections in the Keyboard Shortcuts program: Sound, Desktop, Window Management. In the third, there should be a series of commands
Move window to workspace ...
Move window one workspace ...
and, at the end,
Switch to workspace ...
I know that some distros modify Gnome, but I can't believe they'd leave these out.
The other program that can set these keybindings is gconf-editor. In that, you go to Apps - Metacity - Window keybindings.
You can also do the job manually by editing