When you use tip 4497 » Windows XP can group similar taskbar buttons, items are only grouped when the taskbar buttons get too small.
To change this behavior:
1. Use the Registry Editor to navigate to:
2. Create a new DWORD value name of TaskbarGroupSize and set the data value to:
0 - Group by age with the oldest group first. This is the default behavior.
1 - Group by size with the largest group first.
2 - Group any group of two or more icons.
3 - Group any group of three or more icons.
3. You must log off and log on for this setting to take effect.