there's a article at bit-tech where they used an IC chip to control the color LEDs to light up when they is HDD activity. Perhaps u can mod some wirings and make it so that u can have it powerdown ur neon when ur not using, though u have to have ur HDD at activity mode to have it turned on!
think this is it:
http://www.bit-tech.net/article/83/
didnt mange to get thru to the webby at time of posting, so search ard bit tech if i hit the wrong webby!