[magick-users] Confused with image magick command line

[Novice Programmer]

hello All,

I am new to image magick. i am performing a very primitive taks using Magick
but still failing to do it..
i am trying ot convert image to its 320x240 thumbnail...

Here is the command that i enter:

convert -thumbnail 320x240 test.jpg thumbnail.jpg

and i get the error which says as:
convert : unable to open image test.jpg : No such file or directory
convert : missing an image filename 'thumbnail.jpg'

if i change the command to

convert -thumbnail 320 * 240 test.jpg thumbnail.jpg then every thing works
fine except that i have an image having width of 320 and arbitrary height...

i want to control the height as well... Please help.. what is wrong with the
command which gives me erros..

i am using magick on windows xp.

-- 
Thanks & Regards,
Novice (http://ishuonweb.wordpress.com/).