I have been researching this for a while now and no where can I find a solution that works perfectly in a list with multiple content types. I needed to create hyperlinks on a page where the user could click the link and in modal view the "New Form" would open in modal view for them. I have finally achieved this and here is how you do it...
Use the following code below to create a hyperlink that will open the "New Form" for a specific content type...
You can get the content type ID from the URL in the content type settings under the your sites settings > content types > select the content type
You can also get most of this information if you open the content type form in the list using the "New Item" drop down under the "Items" tab at the top. Select the content type then right click in the modal pop up of the content type form and select "view source" (works in IE). At the top the URL path will contain the Root Folder ID and content type ID.
To get the list ID, the easiest way is to go the list settings. In the URL at the end select the %7B*List ID*%7D. Remove the %7B and the %7D then replace all the %2D with dashes (-).
Insert all this information into the code string above and this should work for you. Also just because someone may get confused, the ** before and after my comments in the code string are not part of the code!