thanks very much.
Can I ask a follow up, just to clarify?
I do not know what a disk image file is. But I take it I should not bother downloading those. I recently downloaded a zip file, and doubled clicked on it but nothing happened. For now, the only other alternative seems to be the sit file. I have a Stuffit programme. I presume that that will be used automatically to open the sit file.

When you say mount it, does that mean put an icon of it in the dock, or on the desktop?

So T3 and ethernet are faster than DSL?