How are you getting on with this?
I'm doing something similar (without the servos, though I am going to try using ws2801s to drive solenoids)
WS2801 control - http://www.bliptronics.com/arduinocode/blip_leds_spi_2801.zip works for me
And artnet - get an ethernet shield (or the cheaper alternative - WIZnet W5100 Network Module with Mag Jack - WIZ811MJ - DEV-09473 - SparkFun Electronics Connected as follows -
J1-1 (MOSI) to D11,
J1-2 (MISO) to D12,
J2-1 (3.3) to 3.3v,
J2-3 (SCLK) to D13,
J2-4 (/SCS) to D10,
J2-9 (GND) to Ground,
J2-2 (/RESET) to Reset
Then download the zip file here art-net set for arduino | vvvv and use the sketch 'art-net receiver.pde'
You may need to change 'the condition from ==taille_chaine_artnet to >25' See this thread - @karistouf re:artnet set - question - Forum
Now we're got here we run into a problem which is both the ws2801 chips and the ethernet controller are using the spi bus. I'm currently trying to figure out how to combine both. I think there's a way do use spi on arbitrary pins but I'm not sure. It should actually be possible to share clock between both and use mosi for the ws2801 and miso for the ethernet controller, as we dont need bi directional communication (unless you need servo feedback)
Where are you based?