Right, we were thinking about making an actual cool flame-tongue sword, since BG2 made it suck, and it'd be nice to have it for Tutu. Anyways, this is what we learned.
The first two letters for weapon animations seem to be WQ.
The third letter is either L, M, N, or S. These seem to dictate which avatar uses them. L is for human males, at least. It isn't for human females. My guess would be that one is for human males, the other for human females, another for elves (both are the same size), and the last for gnomes, halflings, and dwarves all together. Haven't verified it, though.
The fourth and fifth letters are what goes in the .itm file to say what it should use as an animation. SS is short sword, FS is flame sword, S1 is long sword/bastard sword.
The sixth, seventh and eighth letters are indicative of the action the animation is for. Various swings and idle-standing around and suchlike.
Anyways, Sim counted 133 frames in one bam he took a look at, and with numlock and windows calculator at my disposal, I estimated that the total number of frames to be made for a new weapon animation are 5852. Just thought I'd post this now, so it doesn't get forgotten in the mists of time.
As an example, WQLS1A1.bam is the Human Male (L) long sword (S1) attack #1 (A1) animation.