By the way, some versions of Windows and some players have problems with large ( > 2GB) AVI files.
http://support.microsoft.com/kb/939130Microsoft published fixes for these problems so if your Windows installation is a bit out of date you may need to download a fix from Microsoft site.
Please note that iPi Recorder uses custom implementation of AVI so if you encounter a problem in iPi Recorder then it is not related to Microsoft's bugs.
VirtualDub also has custom implementation of AVI so it should not be affected by Microsoft's bugs.
However, your video player may have a problem related to Microsoft's AVI bug. So it is always recommended to install latest service packs and hot fixes for Windows.
Also, you should not use FAT32 or FAT16 as your file system for video files because of potential problems with large files:
http://neuron2.net/LVG/filesize.html