Just a quick tip to keep in mind. As a *general* rule of thumb, you should try to keep your shutter speed higher than your focal length (or something like that.) For example, if you're shooting something @ 50mm, you would want a shutter speed of 1/50th of a second or faster. The 2nd shot you posted was at 1/15th of a second @ 150mm, about 10x too slow for the situation. One thing that could have also helped that shot is upping your iso from 400, although that will start to introduce more noise to the image.
As for IS helping the shot, in that particular case, depending on how many stops the IS system affords you, it very well could have helped that 2nd shot quite a bit, but only because the subject matter was stationary. IS won't help get, for example, moving people shots blur-free as the shutter is still going to be open for a long period of time. If you're going to be doing a lot of indoor shooting, I can't recommend a good flash enough. It's usually the cheapest and most effective way to improve low light shots like that. Fast glass also helps, but comes with drawbacks such as high price tag and hefty weight.
It takes some time to get used to the gazillions of options a DSLR offers, but it'll all start becoming 2nd nature soon enough =)