This is just FYI in case it is of use to anyone.
I got a new Dell system, Windows 7 x64. I disabled Windows firewall and downloaded and installed the latest version of ZA Free. I'd been using ZA for years and liked it. I also installed lots of other software and peripherals, so when I started getting blue screen crashes -- three to six in a day -- I had no idea what was causing them.
After sending a load of system information to some experts on a support forum, and after trying several alternative solutions that didn't work, it was determined that ZA must be the cause of it. So I uninstalled ZA , and no more blue screens.
I know that many others are using ZA Free successfully with Win 7 x64, and I offer my story only for information and not complaint. If anyone at ZA wants the crash data (zipped into a small rar file), email me and I'll be glad to send it.