Not to worry - as I said in my previous message, I can reproduce the error
on my own XP machine.

I also noticed that running test_tarfile alone doesn't trigger the errors,
which leads me to suspect that the failure is due to some interaction with
another test getting run before test_tarfile. I'm currently trying to
determine what this test is.

I suspect that the problem is at least partially caused by the fact that
tarfile uses a default compresslevel of 9 for .tar.xz archives (rather
than the recommended value of 6). According to the man page for the xz
tool <http://manpages.ubuntu.com/manpages/lucid/man1/xz.1.html>, using a
compresslevel of 9 can result in memory usage of up to 800MB during
compression, which is a significant fraction of the bot's 2GB of RAM.
(I suppose it would be a good idea to mention this in the documentation
for the lzma module, so users won't get bitten by this...)