The first part is easier. That can be added the the language files. Version 3 and up have a Define Languages area in the Tools menu. If you click on the page you want to add it to (say, for example, checkout_shipping to add it to the shipping page in the checkout process area), you would add a line like this:
<br>
Your order will SHIP within approximately 7 days. You should receive it within 10-14 days.
to where you want it to appear. In this example, I placed it below the line that says:
This is currently the only shipping method available to use on this order.
If you want it on a different page, select the page you want it on.
To have the check a box would be a bit more work, but not too hard. There is an add-on that allows you to ask customers to select that they have read your terms before checking out. This could very easily be modified to have them confirm that they have read your shipping info. Or, better yet, you could change the check box language to add your shipping info to that line. You can search for the add-on here: http://addons.oscommerce.com/ there are a few that will do this. If you aren't comfortable installing addons, let me know and I'll send you a quote.
