rpm speed is not the only factor in whether the drive will work. I am guessing it is not an SATA, but is it an ATA133, 100, 66 or do you have it as an external? Best thing to do is give it a try. I have a 5400rpm in my laptop and it works. I don't edit at full resolution and frame-rate but it works for what I need it for.
LaCie D2 series. these are some of the best drives ive used. great speeds, send you all the cables, lots of ways to hook em up. can daisy chain em easy. and yes speed does matter. and even in some instnaces, (if you use pro tools) your hard drives internal chips can make a difference between working and not. ( the lacie D2's works great with protools also)
now your slower older drives will work.. but its a matter of how long do you want to wait for them. if your editing 8- 10hrs a day, a few min here and there can loose you and hour or more of work.
but if your just doing a One off and only need it for One project. you can get away with what you already own. just be carefull not to overheat em..
With a dualcore, and 2gigs of ram, you will edit DV extremely well. The bandwidth will only come knocking on your grandmas door when doing 60min timelines.