Well... My focus wasn't so much on the double click, but:
WinXP
1.3ghz AMD
512mb Ram
NVIDIA GeForce FX 5700LE w/ 256mb DDR graphics card
Running very lean & mean for such low specs. Actually, I get better performance with my low end optimized machine than we do with the 2&3ghz machines at work (but the users have a bad habit of running every piece of crud background process that they can find on the net, or install off of their HP printer cd.
)
UPDATE:
Just did a quick test and the bottleneck appears to be tied to the CPU. The dom3 process idles around 43% on the main screen (large map with lots of armies), then upon entering the Army Setup screen, it leaps to 99% and I lose double click in dom3.