Inner Tube runs slowly on my secondary monitor in a two monitor set up.
Complex real-time 3D games are generally required to be run on the monitor set as your "Primary" monitor. If you have a fast enough system (Pentium IV 3 Ghz) with a good recent ATI or NVIDIA system it may run well even on the secondary monitor.

You can either try lowering the resolution of your secondary monitor or switching the primary and secondary monitors (See instructions Below)

Changing Monitor Resolution

Graphical programs may run faster on a lower resolution monitor, especially if they are running on your secondary monitor.

To change the resolution of a monitor:

Go to Start Menu->Control Panel. Either click on "Display" if present or "Appearance and Themes" then "Display" (if you are in category view). Click on the "Settings" tab. Click on the monitor square that shows the monitor that you want to change the resolution of (2 is generally your secondary monitor). Drag the "Screen resolution" towards less to decrease the resolution (may improve program speed). To maximize speed try to get the resolution down to 640 by 480. If your slider bar does not slide that far to the left you can set the resolution in the advanced options (see next).

To change the resolution of a monitor using the advanced options (so you can lower it below 800 x 600)

Open the display properties settings tab (see steps 1-3 above). Click the "Advanced" button. Click the "Adapter" tab. Click the "List All Modes..." button Choose a mode that begins with "640 x 480" or an equivalent low resolution mode. Choosing a high refresh rate, such as 72 instead of 60 Hz can be better for the eyes.

Switching Primary and Secondary Monitors

The easiest way to switch your primary and secondary monitors is by switching the cables running to your 2 monitors.

You can also switch your primary and second monitors in Windows. There are different ways to do this depending on your video card (ATI, nVidia, etc.). Call your video card manufacturer to get help switching your primary and secondary monitor if the following suggestions don't apply to your card. nVidia specifically allows you to keep your taskbar and icons on the secondary monitor.

There is also a piece of software called TigerVista Manager ($75) that provides easy access to primary and secondary monitor switching.

To change the primary and secondary monitor in Windows (many graphic cards disable this windows switching)

Go to Start Menu->Control Panel. Either click on "Display" if present or "Appearance and Themes" then "Display" (if you are in category view). Click on the "Settings" tab. Click the monitor square with a large "2" on it, or choose the display 2 from the Display: drop down. Click the "Use this device as the primary monitor" checkbox. Press "Apply" to apply your change. If the "Use this device as the primary monitor" checkbox is already checked, choose the other monitor and click "Use this device as the primary monitor. If the "Use this device as the primary monitor" checkbox is grayed out (not selectable) you cannot use this standard method. You may have graphics card incapable of switching the primary and secondary monitor (for instance in laptops) or your graphics driver may have an alternate method (see the ATI method below if you have an ATI card).

To change the primary and secondary monitor on an ATI card

Go to Start Menu->Control Panel. Either click on "Display" if present or "Appearance and Themes" then "Display" (if you are in category view). Click on the "Settings" tab. Click "Advanced". Click the "ATI Displays" tab (if this tab is not present you should update your video drivers). Switch the monitors labeled "1" and "2" by clicking the "1" where the "2" is selected or vice versa. Press "Apply" to apply your change.