Over the years I've amassed a collection of old software and machines. This is just my list of what runs well where and why, and occasional other notes about apps.
Written Jan 2009, updated Dec 2009, June 2010.
Overall, there is a new matrix: some things require a new OS, some require Intel, some both. For example, some things will run on 10.4 but require Intel, some will run on 10.5 on either platform.
Mac OS X:
10.0, 10.1, 10.2: run on any G3 with 128 MB RAM. 10.2 has Quartz Extreme. Safari is too old to run anything worthwhile. 10.2 is the last OS X that will run on a Beige G3.
10.3: requires a G3 with built-in USB (iMac, B/W G3). Had a nicely revised Finder (useful sidebars) and came with iChat A/V (a $29 upgrade to 10.2). Safari 1.3.2 is now (1/2009) almost worthless. The newest machines that shipped with it were Mac minis and early G5s.
10.4: requires a G3 with built-in FireWire. (I.E., not some iMacs. Not sure about G3 PowerBooks.) I hate Spotlight. Can run Safari 3 or 4. First OS X for Intel Macs. Worked with Boot Camp Beta, but the beta period has expired.
10.5: requires a G4/867 or better, DVD drive, 512 MB RAM. Time Machine and Quick Look make up for Spotlight, the crappy Dock, and the effed-up Finder sidebars. Comes with Boot Camp. iLife 09 requires 10.5.
10.6: For Intel Macs only. Exposé is better. If you try to eject a disk and it's in use, IT WILL TELL YOU WHAT IS USING IT. Other refinements.
Handbrake:
0.7.1: First Universal binary (i.e., native on Intel)
~0.9.x: requires 10.5
Safari: maxes out at 1.3.2 for 10.3. 10.4, 10.5, and 10.6 all get Safari 4 or 5. Speaking of which, Firefox only goes to 2.x for 10.3. (12/2009 - I've only got one 10.3 Mac left. :-( )
Photoshop 7, Illustrator 10: First that ran natively in OS X. Great for single G4 (notebook, Mac mini). Photoshop 7 was the last version that could be used to edit pictures of US currency. http://www.google.com/search?q=photoshop+us+currency CS is kind of a pain when you work for a textbook publishing company and want to make a Math book.
Adobe CS: Good on a single G4
Adobe CS2: Good on a G5 or dual G4
Adobe CS3: First that ran natively on Intel. OK on a dual G5.
Office 97: Windows.
Office 98: required a 120 MHz PPC Mac, which was kind of a lot at the time. :-)
Office 2000: Windows.
Office 2001: Mac OS 9 (maybe 8 or 7, not sure.)
Office X: native for OS X; almost identical to 2001; my favorite of the bunch overall, other than only supporting 31-character filenames.
Office 2003: Windows. Yawnfest.
Office 2004: Some crappy defaults, like Page Setup view in Excel and formula warnings turned on everywhere; nothing that can't be worked around. Copy and paste works between Excel 2004 and Safari 2 or 3 in 10.4.
Office 2007: Windows. Introduced docx/xlsx/etc.
Office 2008: First version that runs natively on Intel Macs. Ribbon UI.
Parallels 2: Won't run in 10.5. Runs W2K like a champ.
Parallels 3: Claimed to come with better 3D but wouldn't run any of the 4 or 5 old games I threw at it.
Parallels 4: Own, haven't yet tested.
VirtualBox: Great, except that its performance extensions don't work in W2K--only XP and newer.
Win95: Great on ancient hardware, like a P100 with 32 MB RAM. Runs up to IE 5.5.
Win98: Great at 400 MHz/128 MB and up.
W2K: The finest OS Microsoft ever made. Stable and fast. Runs like a Swiss watch on a 1 GHz PIII. OK with 128 MB, great with 256. The first OS that ever ran an ATI capture card stably enough to actually CAPTURE VIDEO.
XP: Ugh. Only when needed. XP + P4 = death.
Vista: Ugh^2. I hear it's OK now. Other than the smallest amount of testing, I have no personal or professional reason to use it. They even screwed up Freecell, turning a nice, simple, clean, FAST game into a Vegas-esque nightmare of glows and other lame effects.
7: apparently fixes problems (real and imagined) with Vista. I hate the new taskbar. I hear there's a way to fix it but I didn't find it in the digging I did. Luckily I've got XP at work, and XP at home as needed, usually in a VM.
iMovie 4: Works with a Sony DVMC DA1 or DA2. Captures in 2GB (9 minute 28 second) chunks. If you trim clips and empty the trash, it creates new, smaller clips and recovers the space. Takes a little time but it's GREAT on older systems with small hard drives. Only works in standard-def.
iMovie 5 (aka iMovie HD): Doesn't work with a Sony DVMC DA1. Captures up to 1 hour at a time. DOES NOT reclaim space when you trim a clip--only if you delete one entirely. Introduced the ability to capture from an iSight.
iMovie 6: Not much different from iMovie 5. Runs natively on Intel. Can be downloaded free from Apple (if you have iMovie 8, not sure about iMovie 9 users) here: http://support.apple.com/downloads/iMovie_HD_6 UPDATE: Gone.
iMovie 8: Radically different from iMovie 6. Supposed to make most editing easier but only achieves that about half the time--many things, such as basic, precise editing, are now much harder.
iMovie 9: Fixes some things that were missing from iMovie 8, like precision editing. I sitll prefer the old style for the simple work I do.
Google Chrome: Requires 10.5 and Intel.
Other than a few Finder bugs, and the fact that Safari has been left behind, my favorite setup (other than a stomping Mac Pro with 10.6) is a dual G5 with 10.3.9, Adobe CS, and Office X.