Ok in your renderlist stands wich codec you currently use. Click on it. A dialog opens.
Under "video output" there is a little button with "format-options" (sry my version is in german). Click the button choose your codec. Choose Lagarith
You can choose all of your codecs there. If both looseless codecs are not avaible than there is something wrong.
... Just a thought. Maybe you can work with looseless .mov (if it can be looseless I don´t know, aks Greg) in Vegas?