Time Machine causing boot and lockup problems

Maybe I'm using it wrong, but

I have La Cie Rugged External HD attached to my 2.4Ghz Al iMac through Firewire 800 for the purposed of being a backup drive through Time Machine. However, about half the time when I start or restart my machine, I cannot get it to boot unless I disconnect the external HD. Also, my machine has locked up a fair number of times recently, and more than half the time it seems to happen when time machine is doing something automatically. Am I doing something wrong? Is there something wrong with the machine? Is there a known bug in the software?

Thanks

Try using USB instead of Firewire.. I had problems with Firewire also, then when I switched to USB things started working again.