When they are talking about the effect of interest rates it is in relation to demand and GDP.  So if the interest rate increases there will be less of an incentive to borrow money because it will be more expensive to pay it back.  So the GDP would go down because people have less money to spend.  An example would be if there are high interest rates on car loans, less cars will be purchased.  

In relation to investments, I would think that what you are saying is correct.  If interest rates go up, people might invest more but that means they are spending less money, which will in turn will make GDP go down also.

Well said sparky9902!!  Simple and straight to the point.