If you are creating charts with SpreadsheetGear, then you are using the IWorksheet.Shapes.AddChart(double left, double top, double width, double height) method. You should be able to control the location as size of the new chart with the specified parameters.
If you need to reposition or resize an already-existing chart, you'll need to set its IShape.Top/Left/Width/Height properties. You can access an IShape object via the IWorksheet.Shapes collection. Example:
// Position top edge of chart 50 points from the top end of the worksheet
worksheet.Shapes["Chart 1"].Top = 50;
// Position left edge of chart 100 points from the left end of the worksheet
worksheet.Shapes["Chart 1"].Left = 100;
The IWorksheetWindowInfo interface has a couple methods that can help you convert zero-based row offsets to Point-based coordinates, which are the units used for the above size and position properties. See RowToPoints(...) and ColumnToPoints(...) for more information on these.