Secunia, a well-known security company, has launched an online checker (at http://secunia.com/software_inspector/) that will "inspect your operating system and software for insecure versions and missing security updates."
I've just tried it and it reckons it has found 10 programs that have security problems. These include Adobe Reader 7.x, RealPlayer 6, Sun Java JRE 1.5.x / 5.x, Macromedia Flash Player 6.x, Macromedia Flash Player 8.x, and WinZip 9.x.
I've going to have to take a deeper look, because I already have Macromedia Flash Player 9 installed. Also, Secunia reckons I have ZoneAlarm 6, which is news to me.....
The main interest in the Secunia software is to double-check whether you have all the Windows Updates correctly installed, and it tells me: "You do not have the following Microsoft security updates installed: KB928090" for IE7.
Anyway, have a go, and let me know if you think it's useful.....
Update: Aha, my son has Zone Alarm installed, and it's found it in his back-up on my USB drive... That probably explains some other entries, too.
