There can be used at a variety of resolutions. The default resolution of the client (There) window is 800x600. If you would like to view There at a different size, follow these steps...
Settings Manager - Inside the client
1. Go to There -> Customize -> Toolbars and Tips -> Settings Manager
2. From this window you can change your window size or switch between OGL and DX8 video renderers.*
ThereTweaker - Outside the client
1. Go to Start -> Programs -> There -> There Tweaker
2. From this window you can change your window size or switch between OGL (Open GL) and DX8 (DirectX 8) video renderers.*
*Note: If you are logged into There at the time you change the video renderer (OGL/DX8), you will need to log out and back in again in order for the change to take effect.
To use windowed mode, the resolution chosen for the There client must be smaller than the desktop resolution. For example, if you use 1024x768 desktop resolution and want to use windowed mode, then you are limited to 800x600 resolution in There. In full screen mode, the desktop resolution and There resolution can be the same value.