A 'Windows Vista' computer would be more apropriate for a trash can project, but it probably would work very reliably...
Anyway, a microcontroller would be more then enough. You could use infrared LED and reciever module to either detect proximity or broken beam, kind of depends on the the trash can. I threw together a proximity detector with a 88 cent ATtiny13, as a first real project. Not too tough.
The voice... there were several threads here about voice recorder chips, might look into those, or a cheap MP3 player.
A hobby servo is pretty strong, might be up to the task of opening some lids, but kind of depends on the can. Took me a while to get the timing worked out to control a servo with the same Attiny13 chip, but I could see it might work with this little 8-pin part.
A Mac would be way more then what you would need, never used one myself, but was tempted (always hated Windows), but the software I wanted to use was mostly DOS, and then Windows, eventually Mac...
Let see what the Pic guys have...