Since actually I don't have WMV, I searched with google for trailers in WMV and one of the first link I found is
Halo Wars trailer. I tried the first one (Low Bandwidth 360p Stereo .WMV 14.9Mb) on my Athlon 900 with 256MB RAM PC133 and IDE disk (with other software running in background) and I had
NO FRAMES DROPPED
Try it and if you haven't them either, then I'll try the one with higher resolution
