so there is no way to cancel the upgrade???
Did you get the same error as you were initially talking about??
EDIT: Also looks like some of you boys owe me some money
EDIT 2!!: Working from the picture and what you have said about the RAM installed (assuming it hasn't been changed since purchase) I have worked out it is an 06 Macbook either 1.83Ghz or the 2Ghz Core Duo one.
Now from that I went to crucial to see the RAM available for your machine. The RAM code matches up with the numbers you have given us. Crucial RAM The link is for the 2.0 Ghz model.
From there I am a bit stuck as I'm not 100% sure that RAM for a 1.83 is the same as for a 2.0. I have a sneaking suspicion it probably is but if one of the other members could confirm that would be good.
From there you could buy just the 512 module for a few quid. Take the other two RAM modules out, put new one in (carefully!!!) and try the same procedure as before to Erase & Install Leopard.
If it doesnt work then its only a few pound. I'm pretty sure its worth a try but input from the other members would be good to maybe sure up what I am saying!!