A tablet usually has two modes, a mouse mode where the pen stylus position is relative to the last position and a screen or pen mode where the pen stylus position is mapped between where the tip of the pen is on the tablet and where the mouse cursor is on the screen. This means that if you have a tablet of my size of about a 3 x 5 active area and a monitor which is about 10 x 16, then a movement of 2 inches on the tablet is almost 6 inches on the screen. Very tiny movements on the tablet are very large movements on the screen in pen/screen mode. The smaller the tablet and the larger the screen, the more the ratio of real movement to cursor movement.
Now, I have two monitors to boot so the area my little 3 x 5 tablet maps to is about 10 x 30. When this happens, left and right movements are proportionally larger than the up and down movements and therefore even harder to deal with. This is why I prefer mouse mode.
But, Gimp and Wacom have an issue with mouse mode and that is what was causing the tablet to not draw in Gimp. So, here are the settings you will need to use to get Gimp to work with your Wacom tablet.
1. In the Windows Control Panel (Start, Control Panel), choose the "Pen and Tablet" settings. Ensure "Pen Mode" is selected and if you have more than one monitor I would suggest you also click "Details" and choose the monitor you will be drawing on to be the only one the tablet maps to.
2. Start Gimp and hit Edit, Preferences and "Input Devices" in the left tree. Click "Save input device settings on exit" to ensure the settings you are about to configure will be used the next time you open Gimp. Then click "Configure Extended Input Devices" and review the settings in that window (you should see the modes of your tablet Gimp supports like the Stylus mode and Eraser mode). Make sure the settings are mapped to "Screen" and not "window".
3. Click "Input Controllers" on the left tree below "Input Devices". Make sure "DirectX DirectInput" is in both columns (click it in the left column, then click the right arrow to copy it to the right column).
4. Press "Ok" and quit Gimp. When you start Gimp back up the tablet should work properly.
To truly take advantage of Gimp and your tablet you need to select the "Brush Dynamics" settings in the Paintbrush options panel. I usually set the Pressure to alter the Size of the brush. Playing with the pressure sensitivity in the "Pen and Tablet" control panel and the settings in Gimp is best to determine your personal tastes.
**(NOTE: This is a bit of an experiment, I am attaching the screenshots which should explain the steps 1, 2 and 3 in this process. I am not sure where or how they will be placed in this entry, my apologies if they are a bit messed up)