Web addresses can get complicated - it's pretty easy to miss a character or two when copying them down. The best approach to always getting the address correct is to use the "copy and paste" features of Windows (or whatever operating system you use) to accurately copy the address into your Internet Resources message. One way to do this is to take advantage of the technique of opening up multiple browser windows.
First, get to the screen you use to compose a new Internet Resources message, and press Ctrl-N. This opens a new copy of your web browser. You can switch between windows using the task bar at the bottom of your screen. Use the new window to visit the site you want to make available within the Internet Resources module. Then use your mouse to select (highlight) the address in your browser's address or "location" bar. Press Ctrl-C to copy the full address to Window's clipboard.
Now use the Windows task bar to switch back to your Manhattan classroom. Click in the Location: box and press Ctrl-V. The web address will get pasted in, without any worries of errors.
You can also use the same technique to copy short sections of a web site directly into the message area of the Internet Resources message, to provide your students with a summary of the site.