Thanks, fuagda. The PCMCIA card that I have in my laptop has both firewire and usb 2.0 ports but I only see disconnection problems with the HD when I connect the enclosure through the firewire port. If I leave it connected to the usb 2.0 port it will never disconnect, no matter how long the idle time is. Because you also mention that you are having problems with the PCMCIA card port adapters, I am more inclined to think that mine can be an issue with the firewire ports too.
I have opted for leaving the HD connected to the firewire port during burns, ripping, etc, since the data transfer gain is considerable. I just have to make sure that I don't leave the computer unattended for a long time after it has finished the work, until I figure out what the other problem is
Thank you and booma again for the feedback. It has been very helpfull.