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I'll start with the good news CC. Yes you will be able to see Saturns rings and the belts of Jupiter and 4 moons of Jupiter. I gather by 60900 that the scope has a 60mm objective and is around 900mm long. If that's the case then you will be pushing it to see real detail. The Barlow increases your telescope focal length ie: 900mm becomes 2700mm. This effectively triple the magnification power of your eyepieces. magnification = telescope FL / Eyepiece FL. SO a 900mm scope with a 40mm lens will give you 22.5 times magnification.
The bad news is you will never see views like they show on the box. For starters except for Jupiter, Saturn and some particularly colourful stars, everything you see will be black and white and shades of grey. Plus you will never be able to get the magnification stated on the box and still be able to see anything. That 675 X mag is using the 4mm lens with the 3X barlow. I would be very surprised if you well be able to see anything clearly even with just the 4mm lens. Your apperture is just too small. As a general rule, for relatively good optic the you multiply the diameter of your objective (in inches) by 50 to get the maximum resolving power. Therefore the most mag that is useful to you is around 125X.
It will probably be an ok scope for terrestrial viewing, the moon, and on fair to good nights, Jupiter and Saturn, but if you really want to look at the heavens above then you need to have either a scope with a shorter Focal Length to give wider fields of view or a scope with more aperture.
How long have you had the scope and what sort of mount is it on?
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