Make sure, your laptop supports USB 2.0 high speed. If you already own an external HDD, do a readtest with HDTune in order to determine the transfer rate as there are some really junky USB chipsets out there. Also, these Benq drives aren't the very best in external enclosures. If anything goes well, you can't expect more than 12x speed.
before i go and splash some money on a new enclosure i though i could try some recycling and use a generic usb2/firewire enclosure i had lying around to build my own box. now is this possible or would the external dvd units have something in their chipset that external hd units dont?
Try your existing enclosure at first. Retail external drives are sometimes equipped with special firmware or optimized enclosure chipsets. Some drives do not need this kind of optimization. Nothing of these is valid for your Benq, so go straight ahead and see, what results you get. As we all are curious, you may also post, what chipsets are used in your enclosure.