If you are fairly certain that you've removed Enterprise Guide but Add/Remove Programs doesn't seem convinced, you can try removing this registry key:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Uninstall\{E0E662A9-EDC9-4C8B-9E84-448646810926}
Note that this is for Enterprise Guide 4.1. All of the usual disclaimers/warnings about editing your registry apply -- be careful!
Chris