There are a couple ways you can go. You can get wl3 or wl II from hai and that will work with some camera and record when triggered. Usually ok to catch a burglar but by no means a full time DVR.
You can get almost any DVR but the HAI seems to be limited on how many cameras you can push out and how to do it, for instant they have to be compatible HAI IP cameras. So it all depends on what you want your end display to be.
I am in the process of building up a dedicated DVR using a geovision card in a pc. Much better I get a full time DVR and all sorts of functionally like object removal and when the dvr see something wrong it can trigger the hai through a set of contacts and then the DVR will email out pics etc. It just takes the functionally away from HAI and the DVR has a much better viewer and dedicated blackberry and iphone apps.
It all depends what your budget it and what you want your end display to be. I am looking to use CQC or something similar for my end display and hopefully intragrate the DVR and HAI seemless in one touch panel hopefully a ipad.
Also don't use IP cans use regular cameras and HAI camera server, you can get much better cameras and wind up spending allot less in the end.