thanks for the comments..
this is done with a Canon 5DII and ex-demo 24mm f1.4 lens (mk1), shooting continuous 8 sec exposures at ISO3200. you can get very similar results with any DSLR, but a slower lens and/or ISO will require longer exposures (more like 30 secs). but that's not a big issue as i have to speed things up a bit in the video processing as the straight 25fps timelapse is a bit slow with 8 sec original exposures. shorter exposures just help to make planes and satellites look a little smoother rather than just a flash in one or two exposures.
i've been working with a few friends on timelapse motion control equipment. i have used my Vixen GP-DX mount for this previously, and just set one axis horizontal and had it ticking over at sidereal rate (if anybody knows how to set a constant drive speed of other than sidereal using an SS2K let me know!). the other problem is that it's a bit heavy when you're trying to set up at weird and wonderful locations often not right next to the car.
my latest incarnation is a nicely priced Bintel Alt-Az mount (from GSO I think). it has small but solid and smooth continuous worm gears on both axes (most alt-az mounts only have about 20 minutes of slow motion control travel). i hooked up an old stepper motor to the azimuth and it currently rotates at 10-20 degrees per hour although i'll soon change the variac in the circuit to give me a greater range.
if you want to see kick-ass timelapse, check out TimeScapes:
http://timescapes.org/
and they have active forums on everything related:
http://timescapes.org/phpBB3/index.php
beware.. this gets addictive..
phil