I've tried to get more information and I've found the following:

• One can use only software that comes with his DVR. Even if other software applications look the same, they are usually customized to work with DVR from a single vendor. There might be exception...
• There is no direct access to DVR HDD over the LAN. May be USB connection can help?
• AVTech DVRs can be managed from Windows only. But they were tested to work
  with Parallels Desktop for Max OS X

Some kind of software can be downloaded from http://211.22.74.18
There you can find AVtech software for 3g phone and pda. I haven't used it and I don't really know whether it is an official source or not. Can't guarantee that it will work. At least make sure to check the software with reliable antivirus software like Kaspersky Anti-Virus or Kaspersky Internet Security.

You should also contact AVTech at
http://www.avtech.com.tw/english/contact.htm
and request software 'coz it doesn't seem to be available on their official web-site. At least I can't find it anywhere.

And you can ask for more help at other forums where people know more about CCTV cameras and DVRs. CCTV forum seemed to have lots of information and experts:
http://www.cctvforum.com/forum-3.html

You should request official AVTech support or visit other web resources 'coz I'm not an expert in CCTV and my conclusion might be erroneous.