making background, need to what size in pixels to make it

ok im gonna make a custom background for my phone but i need to know what size to make it, i read somewhere else it was 480x320, but when i changed the size of the pic to that it is sideways (unlike the screen on my phone). so i need to know if i just need to make it like that, or if those are wrong dimensions. or if i have to make the image like that and and it will stand up straight when i out it on my phone.

normally i would just try it but i dont wanna sync the pic to my phone and delete all the music if it isnt going to work

thanx in advance and sorry if this is a newb question, because i am infact a newb when it comes to the iphone