This is quite possible & there are two approaches to this but both really require the right hardware configuration.
Nero , Roxio and probably others can burn the same DVD to multiple burners at the same time.
Run multiple copies of the burning app burning different DVD movies to different burners.
For (1) to work well it's preferred that both burners are the same as is the media and that each burner is on it's own IDE cable (channel) and both separate from the source (HD).
The way to configure this is to get an add-on PCI IDE controller & connect the HD to that & connect to burners to the IDE Channels on the motherboard. If you've got a serial ATA HD then the add-on card is obviously not required.
For (2) the burners & media can be different but attached the same as for 1. To get decent burn speeds then the sources of the DVDs also ideally need to be on separate channels , ie 2 serial ATA's or 2 PATA HD's on a add-on card. Separate HDs sharing the same IDE channel may work but I've never tried that.
I can burn quite successfully at 8x like this , never tried yet going faster..
Geno has shown you how to do it in Nero. In Roxio you get to check the burners required actually in the burn screen. This for option 1 only.
If burning different copies I'd go the route of creating ISO images & using ImgBurn to burn these. I think the memory overhead is much lower with this.
Hope this helps.