There's a WHOLE LOT of factors at play here, the first and most important of which is what codec is the HDD recording to? Without that, a good strategy can't really be formulated. Is it recording standard def or high def? Is it recording DV, MPEG2, or MPEG4?
Also, you're idea of "just getting a DVD" from him would be OK only if getting it on the DVD doesn't require re-encoding it. If he has to re-encode or transcode it to put it on a DVD I wouldn't take that route (it's like making an MP3 from another MP3). Also, not sure, but maybe you meant just have him copy the files to a "data" DVD, and not for him to make a "playable" DVD.
Like someone else said, editing MPEG2 is not usually preferred. You can do it, but it can be painful and not all software can do it. It can be especially painful with respect to the audio which in all likelihood is in a seperate file from the video (if the HDD recorded to MPEG2).
You really have two main approaches in my opinion: (1) get the HDD into DV, then edit both in DV, or (2) if the HDD was HD, then you could also upres the DV footage to HD, then edit everything in HD (that would preserve the HD quality for the stuff shot on the HD cam).
The other thing to watch out for here is progressive scan vs. interlacing. Make sure you know what each source is. The DV will be 480i, but if the HDD is HD, then it could be 720p or 1080i. So, it's possible you may need to deinterlace one of the sources and work entirely in progressive mode or you may not have to worry about it much because both sources are interlaced.
The key here is to know what codec the HDD used...