InDesign JEPGS exporting at wrong pixel size

In order to export a jpeg and maintain the 160 x 600 pixels you would have to use a resolution of 72 ppi (which is more or less the standard web resolution). Using a higher resolution will by necessity increase the pixels per inch of the jpeg from what you started with. That's just what higher resolution means as you're increasing the number of pixels per inch with the higher value. For web use 72 ppi is usually adequate but if you really need the higher number you could resample the jpeg in Photoshop. For example, if you export the jpeg at 150 ppi from InDesign it would read in Phostoshop as 333 pixels x 1250 pixels. If you resample it down to the 160 x 600 (while leaving the resolution at 150 ppi) the 160 pixel dimension would appear onscreen at a little over 1 inch (150 pixels equals an inch). If you had exported the jpeg at 72 ppi the pixels would stay at 160 x 600 but the jpeg would now be viewed at almost two inches for the 160 dimension (2 inches would equal 154 pixels or 2 x 72). It all comes down to how you want to see the image onscreen.