gdal_translate question

[Robert Denham]

Hi,
I am interested in using the gdal library, and thought I would get
started by having a look at some examples, like gdal_translate. I can
only seem to get this to work for GTiff formats, though I know you
have done lots of work on other formats. Ideally I would like to be
able to translate from img to say AIGrid and the reverse. But when I
try anything other than the default, I get 

0.ERROR 6: GDALDriver::Create() ... no create method implemented for
this format.


I called it like this:
gdal_translate -of HFA -b 1 irvine2.img irvine3.img

Perhaps someone could explain my problem?

Regards,
Robert Denham