Corrupt downloads but not all sites

When I try and download,, mainly zip fieles, from some
sites, the downloads appear to be complete - even have
the correct icon but they are corrupt. Yet, some sites
always work.

And on another site, if I download it with FireFox, delete
it when it completes and then download it again, it isn't
corrupt. However, they always are if I use IE.

To verify it wasn't my ISP or router I download a file on
my main PC and it was corrupt and I then downloaded it
with my HTPC and it worked. I have done this several
times.

To verify if it was a RAM issue, I ran three different RAM
test programs.

1. memtest86 version 3.4: It ran for 8 hours and found
no errors. Version 3.5 kept rebooting my system each
time it started.

2. Microsoft Windows Memory Diagnostic: Did normal
and extended tests twice with no errors found.

3. MemTest 3.8: It did find the errors "copying between
4b93535 and 4b932a3 did not result in accurate copy."
It also received the same error a few other times.
However, I am not certain it works since neither of the
other two found any.

I have also done various tests on my hard drives and
they all passed.


Any suggestions?

MTIA



Here are my system specs.