It's not your 'old' machine the guilty one, D-ViewCam software is really slow exporting.
I found the following utility. It is clearly unofficial and if it works, it will take some time to process the files too. But it's possible it will take less. If you can identify the database files you want to reconvert (maybe you should look at the file creation date) you could give it a try.
http://bliny.net/blog/post/Converting-D-Link-D-ViewCam-DVF-files-to-AVI.aspxStopping DViewCam server (which is demanding) will lower the exporting times.
For the next time:
"Note: The DCS-920 is not capable of Samba recording" 
It's a pity your cams do not support samba recording. This way the cameras would save .avi files to a Samba share (windows share folder over network) while the regular recording on D-ViewCam server worked. You wouldn't need any conversion.
If you upgraded the cams for this purpose and wanted to keep one-two month old recordings you'd have to buy a 250GB disk, install it as the secondary disk on the computer and store there the .avi recordings to avoid putting too much workload on the primary one. Or you could buy a cheap 250GB NAS for the same purpose (network attached storage, it's a little standalone linux server with several functionalities, samba shares obviously one of them) and plug it into the router.