Glad it was some help, Steve. That "Quality" slider eluded me for quite a while too (originally in Irfanview, but also in Photoshop). As you saw, it makes very little if any visible difference on-screen, but it will make a difference on prints, so I always save "fat" and "thin" versions of my good shots. All the shows I've been entering require photos for the jury process, so it's handy having a few good prints.
I can also relate to the differences between the Photoshop versions. I use Photoshop LE V4.0 at the office and a current version of Photoshop Elements at home. The "Elements" edition is a lot easier to use. I've also got Photoshop 7 available at the office, but I haven't gotten around to installing it. My photoshopping at work is limited to screen shots and other simple graphics, so I've not really needed the extra complexity of version 7.