Always download the manual for the board you plan on buying.
The P4P800-VM has no adjustment for the FSB of the CPU, so
it is not an overclockers board. Generally, the full sized
ATX boards have adjustable CPU clocks. (If you can find a
version of "setfsb" or "clockgen" that can program the clock,
then you can overclock it, but those kinds of programs must
be custom designed for each motherboard.)
http://www.asus.com.tw/support/download/download.aspx
ftp://ftp.asus.com.tw/pub/ASUS/mb/sock478/p4p800-vm/e1338_p4p800-vm.pdf
P4P800 boards with the 865PE on it, have an issue with
video artifacts, when running with CPU clocks greater
than 200MHz (FSB800). You can see the data here. I haven't
checked this thread for a while, and perhaps someone has found
a good brand of RAM to help with the problem.
http://abxzone.com/forums/showthread.php?t=62275&highlight=artifact+p4p800
You can search the model names of the boards here, and
see if there are any other issues.
http://www.abxzone.com/forums/search.php
I bought a P4C800-E Deluxe with an 875 on it. I didn't buy it for
all the built-in peripherals - I wanted a board that wouldn't
have issues, and I've been happy with it so far.
In terms of how overclockable the processor will be, check this
web page, as it is a database of overclocking results. It can
be difficult sometimes, to figure out which processor is which -
if you get the SSPEC entries from the page for a processor,
you can run the SSPEC number thru processorfinder.intel.com
and get more details on the processor model in question.
I don't see CeleronD listed here, so maybe this will be a
waste of your time:
http://www.cpudatabase.com/index.cfm?Action=search
Asus microATX boards are intended for system builds who
are making 100 identical computers for a small business or
office. The boards are not really intended for enthusiasts.
It is a shame, as some people want to build HTPC systems with
some of these boards, and it wouldn't really kill Asus to
add a bit more stuff to the BIOS (as they write full featured
BIOS for their other boards anyway, and it is largely the
same code for all members of the 865/875 family).
HTH,
Paul