Problem with video after muxing ac3 audio

[Principle]

I encoded my video divx 3 SBC and its fine however when i mux in the ac3 audio the video jumps im pretty sure its not my PC speed AMD XP 1.6 with 256 DDR ram.

If i mux in a mp3 all is well its just when i add the ac3 that it jumps can any one recommend anything that might help.

Thanks this is driving me mad.

[Principle]

sorry guys iv fixed it changed the interleave to 64ms instead of 1 frame works fine now guess i should have paid more attention to the guides.