Just checked the vBulletin code list but found nothing related to img size. Tried [img=640x480] but it doesn't work.

Is there a way to manually set the size of an img ?

upload it as an attachment instead of inserting it into the post?

use windows, and change desktop resolution

Quote from doyal :

use windows, and change desktop resolution

^^ this.

I have asked for the image resizing mod many a time, but we still don't have it

Upload onto imageshack and tell it to resize the image