MacBook 2,1 (the original BlackBook)
Mac Model: Macbook 2,1 (black, purchased after 11/2006 C2D refresh)
Operating System: 10.5.8 (SC2 played in Windows XP Home 32-bit)
Processor Speed: Intel Core 2 Duo T7200 @ 2.0GHz
RAM: 4GB DDR2 @667MHz
HDD: 200GB Hitachi 7,200RPM
Video card: Intel GMA 950 w/ 64MB memory in OSX and 224MB memory in Windows XP
Screen resolution: 1280x800 / 1280x720 in SC2 (defaulted to this)
Default settings:1280x720, Low settings, 2D portraits
Modifications to default settings: None (as of yet)
Playability: Extremely playable (in XP), I was amazingly surprised. It will install and run in OSX however the screen will remain blank as Blizzard has not released a compatible video driver for the game to run on the Intel GMA 950, if there is anybody in the community that writes drivers this game is playable on this system and video card at about 24FPS and 14-18FPS in combats, I'm sure there are still a lot of these systems out there. I would recommend upgrading to 4GB of RAM and a 7,200RPM HDD if you haven't already. I'm not sure how well this game would run on less than 3GB of RAM and a 5,400RPM drive.
Since we're talking about older hardware - It does default to high+ on my vista machine running 2.4GHz Athlon x2 (939 chipset), 2GB DDR400, 7,200RPM HDD, 9800GT running at 1400x900 resolution (default 19' Widescreen resolution). So if you're running something similar you should have no problems. It defaults to ultra+ on my XP-64bit machine running C2D 2.66Ghz, 4GB DDR2 800MHz, 10,000RPM HDD, dual Radeon 4850's.
Hope this helps.