I have an easy answer and a harder answer:
Easy Answer
You can simulate almost any NI instrument in MAX. Right click the Devices and Interfaces item in the left pane and select Create New... Unfortunately, this limits you to whatever the driver designer thought would be a good signal. It is good for simple testing, but you will rapidly run into its limitations.
Harder Answer
Use LabVIEW classes to make a hardware abstraction layer. This my seem like an advanced topic for a beginning LabVIEW programmer, and it is, but it also neatly solves the problem of switching between simulation VIs and real acquisition VIs without writing a bunch of switching code. In short, you create a LabVIEW class which has the interface you want for you data acquisition. This can be your simulation code. You then create a child class which has exactly the same interface, but uses the DAQmx/NI-SCOPE/NI-DMM/etc. that you really want to use. Switching between the two is as simple as selection the class you want to use at run time. This is a lot of info in a short time. If you want to go this route, read the LabVIEW help on LabVIEW classes and work through the examples. I would encourage you to do this, since the sooner you learn how to effectively use object-oriented LabVIEW, the easier your life will be.
As a further bit of information, most of the measurement instrument groups (e.g. NI-SCOPE, NI-FGEN, NI-DMM, etc.) allow you to simulate an instrument if you use the open with options VI instead of the standard open VI. The inputs are rather arcane, but get the job done.
Let us know if you have further questions.
