MPEG4 is still pretty new. Have you tried MPEG2 level encoding and see if that helps?

------------------
Earl of the OC Crusaders

P3 700@980 (140x7.0 1.85V--dropped from 1001 to o/c video higher)
Abit VH6-II w/256MB PC150 (2-2-2)
Radeon 64MB VIVO 205/205
SBLive! Value
13.5GB & 30GB Maxtor ATA100 (5400RPM)
Memorex 36X CD-ROM/TDK 8x4x32 CD-RW