Scott:
A brief overview.
In the Parameters script, you will need a line of code like:
Values "Cond_Type" "new", "existing", "demo"
where
Cond_Type is the name of the parameter and the other names in quotes are the text options you want to appear in the parameter pop up list.
Then in the 2D script, you will need conditional statements like:
If Cond_Type="new" then Gosub 10
If Cond_Type="existing" then Gosub 20
If Cond_Type="demo" then Gosub 30
where you can define the appearance of the part in the subroutines called here.
There are other ways to structure options within the code (If/Then statements), choose a method that makes sense to you. Also, if you can find an existing library part that shows options in a way that is similar to what you desire, then use that code, substituting parameter names and subroutines that fit your needs, so you don't end up reinventing the wheel.
Hope this helps.
David