Avi problem

Hi guys n gals, say i have a sequence of 1000 bitmap images grabbed at times dependent on processor activity...image 1 grabbed at 0...2 grabbed at 72....3 at 125...27 grabbed at 450...1000 grabbed at 4509. Thats just an example...purely hypothetical figures. If I know the total time the captures took...I divide the number that time by the number of images to get a ''framerate''. So far with CRAZY tweaking I can maintain integrity of audio to sound until about 8 mins...but after that the two slip out of sequence...I''m writing in visual basic....how the heck can I maintain the integrity/sync? Thanks in advance...I''m new to this asking questions and don''t know exactly what information u''ll need to help me. But please do try. Thanks, Daz By the way...trying to create a consistent avi with audio