Assuming you're using 64-bit Windows 7 and 64-bit Java 7:
1) Push [Windows_key]-[Pause/Break] or go to Control Panel > System
2) Click Advanced System Settings on the Left.
3) Go to the Advanced tab and click Environment Variables... at the bottom right.
4) In the System variables box, scroll down to find Path, select it, and click Edit...
5) Under the Variable value, add ";c:\Program Files\Java\jre7\bin" (no quotes) to the end of the line. You may need to change that directory name, so I suggest making sure that directory exists before doing this. It should be the directory with java.exe in it.
6) Use the OK buttons to back all the way out, and close Control Panel.