For video editing, at the very least I would recommend a 7200 RPM Hard Drive of suitable size (60 GB is pretty cheap these days, i.e., less than $150).
If you have a few $$$, I would get a Promise RAID card(http://www.promise.com) and an extra HD. This setup allows you to read and write from both drives simultaneously, doubling hard drive speeds. Assuming 80GB-100GB drives, this would cost you around $400-$500.
As an alternative you can pick up a Maxtor 80GB external firewire drive or similar for under $300. The advantage not only 400MBPS a minute transfer, its portable. Operates on its own AC power supply.
Just to clear up a possible point of confusion. IEEE-1394 (nee Firewire or iLink) maximum transfer rate is 400 MbPS (notice the lower case "b").
Many people don't realize the difference between a lowercase "b" and an uppercase "B". A lowercase b means bits, an uppercase B means bytes. There are 8 bits in a byte.
Futhermore, communications speeds (i.e., modem speeds, serial port speeds, IEEE-1394 speeds) are measured in bits.
Hard drive speeds on the otherhand are measuered in bytes.
So 400MbPS is really 50 MBPS.
Compare this with an ATA-100 drive which has a max transfer rate of 100MBPS.
However, this is a rather moot point since most modern drives don't even approach theoreticaly maxes and all DV editing requires is a sustained transfer rate of 3.6 MBPS (not a problem for most 7200 RPM drives). Some kinds of analog editing require greater transfer rates and that is where a RAID setup has an advantage.
However, if all you do is DV editing, wvg's recommendation of a IEEE-1394 hard drive is a somewhat pricey, albeit extremely easy to install and flexible solution.