Some window managers set up a virtual desktop that's larger than the physical screen. At any given time, you see a viewport onto that large desktop. A window can be larger than the screen, and panning over the viewport lets you pan over the window. I think this is the feature you're looking for. It's fallen into disuse somewhat: most modern environments instead have workspaces that are conceptually disjoint and where a window is only present on a single workspace. But the feature still exist in many window managers. I'll mention a few.
Vtwm was the first widespread window manager with a virtual desktop feature. It used the viewport concept. Vtwm is still available, but if you're used to modern window managers and destkop environments, Vtwm will probably feel hard to use (in particular, it uses focus-follows-mouse, not click-to-focus) and look ugly.
Fvwm is a very configurable window manager. It can be used with GNOME. It offers both viewport-type virtual desktops (a rectangular arrangement of screen-sized viewports, with windows being able to span multiple desktops) and workspace-type virtual desktops (independent workspaces, with windows on a single workspace). You can set the number of viewports with the DesktopSize command. You can navigate between viewports and set the viewport coordinates to a fractional value. The FvwmPager module provides a visual pager to move between desktops. For your ~/.fvwm2rc:
DesktopSize 2x3
Module FvwmPager 0 0
Sawfish is an extremely configurable window manager, limited only by your ability to write Lisp code. It can be used with GNOME. It offers both viewports (called viewports) and independent desktops (called workspaces). The pager add-on provides a visual pager to move between viewports and workspaces. For your ~/.sawfishrc, to use viewports:
(setq viewport-dimensions (cons 2 3))
(move-viewport 0 0)
(require 'pager)
An alternative approach with Sawfish would be to show the same window on multiple workspaces, at different positions. Sawfish supports this, although I'm not sure if the functionality is exposed in the default interface. (I use sawfish, but with a heavily customized interface.) Workspaces are conceptually organized on a line (but you can configure the pager to show them on multiple rows) and are usually set up to be created dynamically.