I was going to suggest "make new window with URL…" (or something like that) but looking in IE's dictionary (Project Builder has rather a nice way to do this) gave me this:
OpenURL: Retrieves URL off the Web.
OpenURL string -- Fully-qualified URL
[to file specification] -- Target file for saving downloaded data
[toWindow integer] -- Target window for resource at URL (-1 for top window, 0 for new window)
[Flags integer] -- Valid Flags settings are: 1-Ignore the document cache; 2-Ignore the image cache; 4-Operate in background mode.
[FormData anything] -- data to post
[MIME Type string] -- MIME type of data being posted
so you could use:
"
tell application "internet exploder"
OpenURL
http://www.foo.com toWindow 0
end tell
"