render_to_string undefined??

Do I need to include anything special in order to call
render_to_string from the view? When I try to do something like this
in my rhtml template:

<%= render_to_string(:partial => "user_description") %>

I get the error:

undefined method `render_to_string' for #<#<Class:0xb76e9134>:
0xb76e910c>

followed by an excerpt from my template. Do I have something wrong
with the syntax?

Thanks,
       --Paul

I think I have found the answer-- apparently in the view templates,
you just call "render" and not "render_to_string". The explanation
for this is probably that in the view you always want to render to a
string, but I'm not sure.
         --Paul