I'm thinking of buying an IDE->usb2.0 cable adaptor which would connect to a a cheap pc internal dvdrom drive for playback of dvd movies on my laptop.
I'm wondering whether there would be no audio when watching dvds because the 'audio out' port connector is not attached to a soundcard.

Now i'm thinking whether getting an external case for the dvdrom drive would technically produce the same result.

Anyone to clear my doubts?

You don't need an audio cable since the data cable carries the audio signal, this goes for both internal and external drives.

How would the external drive be powered then?
Does USB cable carry enough power??? I do not think it does... is there an outsode power source?

I think the cable carries the audio only in XP O/S... I could be wrong.

An external drive would definitely be powered by a seperate power adapter.
I was thinking of getting the the ide/usb adapter as its a cheaper solution than getting an external 5.25" case for a dvdrom drive. The bundle is consists of the cable adapter and power supply. So i was just worried about movies playing without sound
With the drive bare, i dont have to worry much about it overheating. Some external cases are made of plastic and actually trap heat within the drive.

Unless it's a notebook enclosure, most if not all 3.5", and all 5.25" ext. enclosures use AC power.
Check out the aluminum kind, they're pretty good at dissipating heat, even w/o a fan, since the whole enclosure act as a giant heatsink.

Just seen some of this on ebay. Not bad little kits, interesting idea. I wish they were firewire though, to be somewhat more stable than USB2.0 and I guess these are nice becayse you can buy any Optical drive and use it almost anywhere you go.

//me wonders if the drivers are native to XP

Nah, WinXP doesn't come w/ USB 2.0 drivers, that's provided on the mobo's driver CD.