Using IE, how can I set it so that a second window it opens as a tab, not a brand new window?

There are several ways to get a page to open in a new tab instead of a new window:

1) Use CTRL-T to open a new tab, then navigate to the page you want to load (using a typed web address, or favorites/bookmarks)

2) Press the CTRL key while clicking links or click on the link with the middle mouse button. Click any tab with the middle mouse button to close it.

3) Press ALT+ENTER from the address bar or search box to open the result in a new tab.

See the link in below in the "sources" area to get more information on tabbed browsing in IE.

-T