To create a trajectory plot with multiple XY pairs in Excel 2007, you can follow these steps:

1. Select all the data you want to include in the scatter plot, including the column headers.
2. Click on the "Insert" tab in the ribbon at the top of the screen.
3. Click on the "Scatter" dropdown menu and select the type of scatter plot you want to use. For example, you might choose the "Scatter with Smooth Lines and Markers" option.
4. Excel will automatically create a scatter plot with one series for each column of Y values. However, all the series will use the first column of X values. To fix this, right-click on the chart and select "Select Data" from the dropdown menu.
5. In the "Select Data Source" dialog box, click on the "Add" button under "Legend Entries (Series)".
6. In the "Edit Series" dialog box, enter a name for the new series in the "Series Name" field.
7. In the "Series X values" field, click on the small icon to the right of the field and select the column of X values for the new series.
8. In the "Series Y values" field, click on the small icon to the right of the field and select the column of Y values for the new series.
9. Click "OK" to close the "Edit Series" dialog box.
10. Repeat steps 5-9 for each additional series you want to add to the chart.
11. Click "OK" to close the "Select Data Source" dialog box.

Your scatter plot should now display all the trajectories you want to plot, with each trajectory represented by a different color or marker style. You can customize the appearance of the chart using the formatting options in the "Chart Tools" tab of the ribbon.