Question regarding "bad" ram stick

I recently put together an upgrade system from parts which came partly
from ebay. I got a MSI K8T Neo-2F and Athlon 64 - 3000+ from mwave
new, and paired that with a 1GB stick of generic used ram from ebay.
It appears likely the ram has a small problem.

When I run memtest86 on this setup, there is always an error at two
locations on this stick, no matter what timings I have tried. Mind
you, before I updated the bios there were some other flaky things
happening here (i.e., XP only acknowledged 256MB of the 1 GB to exist,
although other programs such as CPU-Z would list at 1 GB). But only
memtest86 has ever given me a problem here. I have another memory test
that runs under XP, it will run all day w/o error. If I do not
overclock, Prime95 will run all day with no error.

Can I just use this stick w/o problems? I have yet to notice much
problem here, just the memtest86 error. I also have a stick of Kbyte
256MB from Staples, it runs MUCH worse with MANY more errors than this
generic stick.

Are there any other things I can try here? Any other memory tests to
cross-check this result?