I am going to give a brief procedure that may help. On the dtasheet there are usually internal schematics of the component. Sometimes you can take this schematic and enter it into Multisim. Once it is there, take HB/SC connectors and place them on all the inputs and outputs and label them to the corresponding pin number on the IC.. Export the netlist. It will be saved as a .CIR file. Open this file and add a line at the very beginning .subckt <model name> <pin numbers>. This would be like .Subckt ICName 1 2 3 4 5 6 7 8. At the very end of this file place .ENDS. This completes the model making process. Now go through the component wizard and when it requires you to load a spice model file, then use the .CIR file you just created.
This is the way I create components that I can't find a model for. This isn't always possible to do because there are a lot of time that the datasheet doesn't contain enough information in order to do this. But for the ones that do, this technique works great. The only problem area is that you do not really know the internal component parameters (if you can deduce this from the datsheet and can find a simular component in the database then that would work better) and most of the time you will have to use ideal components in the creation of your part. This may not produce a truly accurate representation of the particular IC, but may get you close enough in order to simulate it.
I hope this helps some.
