There is an insert page to download, that adds to your manual.
http://dlsvr03.asus.com/pub/ASUS/mb/socka/kt333/a7v333/ie1010_a7v333.pdf
It says:
"Three (3) sockets are available for both 266MHz-PC2100 or 200MHz-
PC1600 DDR DIMMs to form a memory size of 64MB to 3GB. Only
two (2) DIMMs will support 333MHz-PC2700; if more than two 333MHz
DIMMs are installed, the system automatically reverts to a maximum
speed of 266MHz."
Apparently, that slowdown from DDR333 to DDR266 is BIOS version dependent.
It is possible it won't happen with the later releases of BIOS.
The problem with having three slots on a DDR memory bus, is it is
loading dependent. The electrical signals look their best with one
stick of RAM. As you add RAM, the signals get worse and worse.
Driving three double sided sticks is the worst.
The above fix, slowing down the RAM clock, gives extra time for the
electrical signal levels to stabilize, on each clock cycle.
You choices are:
1) Use a memory configuration that has one or two sticks of RAM.
Either buy a quality single 1GB module, using 64Mx8 chip type,
or buy 2x512MB DIMMs. You could even return the 256MB to
Crucial, get a single 512MB DIMM from them, and run 1x256 + 1x512.
2) Slow down the memory clock. Look in your user manual and the
BIOS setup screen, to figure out how to do it. On motherboards
where the memory speed cannot be adjusted separate from the
processor FSB, this means a slowdown in computing performance,
and is why this might not be an acceptable solution. (I think
I see an option to run asynchronous in your manual, so maybe
you can use FSB333 and DDR266 settings for example. I don't
know what your processor's FSB is, so that is just an example.)
Also, experimenting by running Quicktime and waiting for a crash,
is not a good way to determine your memory and CPU are happy.
I recommend two free test tools. Memtest86+ from
www.memtest.org
will prepare a standalone boot floppy for you, and once the
computer is booted with that floppy, you should run the test
error free for at least two full passes. The second tool is
Prime95 from mersenne.org . Prime95 runs in Windows, and has
a "torture test" as one of many options. The "torture test"
carries out an extended calculation, with a known answer, and
thrashes both memory and CPU. Bad memory will error out in half
an hour or less. You can run that test overnight and see if
it will run error free - make sure the cooling on your
computer is adequate for the job, as Prime95 will make the CPU
get hot. Use Asus Probe/Speedfan/MBM5 to check the CPU temp
during the first 15 minutes or so, and stop the test if things
are getting too hot. If your cooling is good, there shouldn't
be a problem running the test for longer periods.
Once you pass those two tests, running Quicktime should not
cause any more problems.
Paul