I was searching the net and found that the biffv1 files are from Baulders Gate, a thing from the site:
One of the primary file formats are that of BIFFV1 (extension .bif). These files are resource-files of the type that became popular with the .WAD files of Doom et al, in other words, the act as a container for other (much smaller) resources. It is obvious that the bif-files of BG are to remain static and that they will not be affected by patches. For one thing, they mostly remain on your CD :-), but I was thinking more on their structure; having the catalog at the top of the file, something which is a really bad idea if you want to add entries. Instead there's an override directory which when a resource is sought will get searched first, only if the resource is not found there the game will reach for the bif-file.
One common BIFF is the AREAxxxx.BIF. These files contain the basic information about an area, three smaller BMP images of which is probably used for the sound-system (very smooth but crude approximation of the area layout), one is used as a map over where you can walk (looks hand drawn) and the last one.. well, we don't know. You will also find a couple of other chunks, and at the very end, all the graphics for the map as seen by the player (we've got some info on the format of that, stay tuned).
What BIFF stands for? If it is an acronym, it could stand for Baldurīs Gate Interchangable File Format
This is what we know about these files.
The site can be found http://gazonk.org/~eloj/gamehack/baldur-old.html
There is a newer site for it aswell