Finder crashes with External Drive on Sleep Mode

I purchased my new iMac 21,5" less than a week ago, and I haven't had a problem with it except for one that it's been bugging me a lot.

I have a LaCie 1TB Quadra d2 external drive that I use to store footage (since it's HD, the filesize won't fit in my 500TB internal hard drive), but I noticed that sometimes when LaCie external drive enters in Sleep Mode, the Finder freezes and the only two ways around this, is to force reboot, because the Finder won't answer and won't open again, or unplugging the external drive without ejecting him first, which it's not safe for me to do, because I'm afraid of hurting the device, and the files in it are pretty important.

This happens almost everytime, especially after a long time on sleep mode. I usually leave Final Cut Pro transferring files all night (since it takes a long time) so I kinda need the sleep mode, but when I wake up, Finder and Final Cut Pro won't answer.

I updated to Snow Leopard 10.6.8 on day one. Is there a way to fix this? Is it normal? I read somewhere that some users were having trouble with external drives on Sleep Mode, but I can't seem to find any further information about this problem.

Thanks!