Well, I'm pretty new at this too, but I think can help you. I looks lke your coming from InkFrog, and its different here. So let me try to be more clear, because you got it a little wrong.
You can't put any value into the image tag to adjust the size. Instead use the [IMAGE1_URL] tag, which puts the URL for the image in there for you...you don't have to manually insert the URL for each image. Then add your width to the HTML. So instead of
<A onclick="document.picture.src='[IMAGE1_600]'; return false;" href="#" ;"><img src="[IMAGE1_50]" hspace="1" vspace="4" border="0"></a>
use this
<A onclick="document.picture.src='[IMAGE1_URL]',width='600'; return false;" href="#" ;"><img src="[IMAGE1_URL]" width="50" hspace="1" vspace="4" border="0"></a>
But...here's the problem I'm having with my own templates...
Since you use [IMAGE1] earlier in your code, you cannot use [IMAGE1_URL] later in your code...it only allows for one type of image tag per image.
Although, the [IMAGE1] tag in Auctiva creates a 'click to enlarge' feature for you...but you have to use their sizing, which is 400x300 thumbnail.