Would Linux be better for them such as Zorin or Ubuntu in terms of speed and security.
Yes. At least I can vouch for Fedora 15, 16, 17 being faster than 10.5.8 or 10.6x on a Core2Duo Macbook Pro.
As for security, yes in that the vector for exploits on linux are less, because they won't have things like Java or Word or Acrobat. And desktop linux specific attack vectors are slim, just as they are on Mac OS. 10.5.8 is no longer getting security updates. So you'd need to move them to 10.6.x at a minimum to get them current security updates.
(They do bank and buy online often) or would I be better off getting them on Lion or snow leopard though the resume feature would be a nightmare since they never close any app and seldom restart. Thanks for any help!
Either way, I suggest Last Pass for their online password management. The top three things about it: 1.) Free. 2.) Cross platform and all browsers. 3.) You get syncing of your password database, just by installing the browser extension and authenticating your account.
So should you need to migrate them to a different browser, or back to some flavor of Mac OS, you don't have to deal with password management or migration.
You could try this out yourself workflow wise using Virtual Box (free, or if you already have another virtualization package), you can check out one of the Ubuntu LTS releases, or even a very secure fast and conservative approach would be CentOS 6.2. This is a free variant of Red Hat Enterprise Linux, that's virtually binary identical to the RH product. It will have security updates through 2020.
Another possibility if you want the latest and greatest browser technology, but on a platform that could vanish almost without notice, is Chrome OS. It's linux at the base, but the GUI is entirely the Chrome browser. You can install LastPass on it for each user to have their own password database. And they can have their own login accounts, so they can have their own browser customizations including bookmarks. But it is only a browser. While it works well in a VM and for the hardware it was designed for, I'm not sure how well it works on actual hardware like a Mini.
Anyway - some options. It's an interesting question. I would like to do this for my parents as well, but a complicating factor is they have iPods and thus need iTunes. And while I'm adept at linux in other contexts, using its applications is not one of them (like the open source equivalent for iTunes and migrating all of their music of to linux).
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Chrome OS builds for Virtual Box are
here.
The USB stick option will very likely not work on a Mac, because "foreign" OS's are pretty much relegated to using Apple's CSM-BIOS for booting, which doesn't support USB devices for booting.
