External firewire drive a bust?

I bought a 120gig Western Digital firewire external drive. Now, it's not the fully external one made by WD. I got a little cheap and instead I went to www.goroyalpc.com and bought a 120 gig internal WD drive put in an ME-320 Series external enclosure, with an IDE-IEEE1394 interface. (This was about $100 cheaper than the WD dedicated firewire drive.) Anyway long story short, I plugged the sucker in and it seemed to be going great but it can't play back my digital video in Adobe Premiere for more than a couple of minutes without stuttering!

Now according to the specs at Royal PC this puppy "Supports serial bus data transfer rates of 100, 200, and 400 Mb/sec." I confess I'm not sure how this translates to megabytes/sec but I know that for full resolution DV I need sustained transfer rate of about 4 Megabytes/sec. My internal IDE drive seemed capable of that. This baby does not. Two questions: 1) Is it possible that this is just because of the IDE/IEEE1394 interface in the drive that slows things down; 2) Is there any possible way to remedy this?

I'm a little pissed because this drive is being marketed as adequate for DV. But apparently it's not, unless I'm doing anything wrong. If it can't support DV playback it's essentially useless to me. If no one has any advice I guess it will be RMA time, and then I'll go get a good old fashioned internal IDE hard drive.

Here are the specs at Royal PC: http://www.goroyalpc.com/product.a [...] ces#detail

My system is a PC (Shuttle motherboard, 512 megs RAM, WinXP Home edition), main hard drive is a 40 gig IDE IBM Deskstar.