Ahhhhhh - I seeeee.
You have a Fat32 Hard Drive system - either because you are using windows 98 or because you never formatted to NTFS on win2k or winXP.
Fat32 drives have a filesize limit of 4 gig. To solve this problem either:
a) Manually export your video in two sections and use the "append avi" option in virtualdub to put them together again.
b) Use the premiere frameserver from
www.videotools.net to avoid having to make the huffyuv file as you can use it to frameserve directly from the timeline. You can also use this to link to virtualdub and make a segmented file if you still want to make a HQ file for archiving.
c) reformat the drive to NTFS