AFAIK it isn't a python/Zope problem but a filesystem problem. I remember to have heard somewhere that Ext2 (the filesystem that Linux uses) only support a file size of 2 GB. Perhaps some of the guru's inhere can correct me if I am wrong.
The solution to this problem - I think - may be to switch your filesystem from Ext2 to ReiserFS.
Ext2 is fine with large files. The problem lies in the virtual memory system of Linux 2.2 or lesser kernels (by way of the C libraries, I believe). With a 2.4.x kernel, ext2 can deal with very large files. But I would suggest going to a journaling filesystem anyway. My favorite is SGI's XFS. It can be a pain if you don't have tons of empty disk space, but it's fun to kick over your machine while it's running and get a fsck in milliseconds. --jcc (no more fscking)