Sure, you can use an <iframe> element to do that.
Edit the cell, edit the "HTML" and insert this:
<iframe src="http://path-to-the-page"></iframe>There are various attributes you might (and probably do) want to add, like
frameborder=yes (or no) to add or remove a border,
scrolling=yes (or no) to add or remove scrollbars. Also,
height=300 and
width=500 (as examples) to set the height and width of the iframe.
Another trick I like is to use the "zoom" style attribute, which allows you to scale the webpage inside of the iframe. Here's an example:
<iframe src="http://www.thetournamentdirector.net" style="zoom: .5" width=1000 height=600></iframe>Note that the zoom factor affects the height and width attributes. So, since this shows the TD site scaled down to 50% (.5), I had to double the height and width to get it to display at 500x300 pixels.