I got a P4 805 CPU/ECS P4800PRO-M bundle from Outpost.

This MOBO takes DDR400/333 DDR SDRAM or DDR2 533/400 DDR2 SDRAM. I updated the BIOS and put in two 1GB Kingston PC2-4200 sticks (533MHz) and things seem to run well but ... slow.

I've fouund that by removing one of the two sticks, file system and memory tests using Sisoft Sandra improve by 50%!

I suspect that I may need to tweak the memory settings or maybe this MOBO doesn't tolerate 533MHz RAM and maybe I should try some 400MHz RAM

Any suggestions would be welcome.

Memory settings being wrong in the bios doesn't account for the magnitude of your problem.

According to the Kingston site, you should be using either:

2 - KVR533D2N4/1G 1GB 533MHz DDR2 Non-ECC CL4
or
KVR533D2N4K2/2G 2GB 533MHz DDR2 Non-ECC CL4 (Kit of 2)

If you're not using one type of those two specified module types, you bought the wrong ram, as in they are incompatible with that mboard, obviously especially when both are used.

If you are using one type of those two specified module types, make sure you have them in the right slots - e.g. singles go often go in certain slots, matched pairs go in others.

I have 2 - KVR533D2N4/1G 1GB 533MHz DDR2 Non-ECC CL4.

This MOBO has 2 DDR2 slots. When using both sticks, both slots are populated. When using only one stick, only one slot is populated.

The ram you have should work fine in this mboard model.
You could test the ram, e.g. using Memtest86, with both modules installed, but I doubt there is anything wrong with the ram.

I assume you have already done this - if not, do it! :

After you make a clean install of an operating system (or do a Repair Setup of an existing XP installation on a drive to set it up for a mboard change) you must load the mboard drivers from your mboard CD, especially the main chipset drivers, in order for Windows to properly recognize the mboard.

If the settings in Bios Setup - CPU PnP Setup - have default settings, there is nothing else I can see in your mboard manual to set.

What is probably going on here is the L2 cache on the CPU can't cache all the ram if you have 2gb of ram installed, but it can when you have 1gb of ram installed. If that's the case, 2gb of ram will run a lot slower than 1gb will, and there is absolutely nothing you can do about that. On many mboards you can install more ram than the cpu's L2 cache will handle.
....

Also - if you installed a graphics card.....

Bios Setup
- make sure Plug and Play Setup - Primary Graphics Adapter is set to the type of graphics you are using.

If you are using the onboard graphics, you will get as much as double the memory bandwith if you install a graphics card instead - sharing ram with onboard video can as much as halve the memory bandwidth. Sisoft Sandra can show you the difference - any video card, even an old slow one, compatible with the mboard will do to test with.

I tested my RAM with Memtest86 and it passed with no errors.

This was a clean install with a newly purchased copy of WINXP Home. The installation was seamless. The MOBO drivers have been installed, first from the CD that came with the MOBO, then from drivers that I downloaded from ECS.

"What is probably going on here is the L2 cache on the CPU can't cache all the ram if you have 2gb of ram installed, but it can when you have 1gb of ram installed."

??????????????????????

This CPU has an L2 cache of 2x1MB. Please explain your statement.

See Response 3 and 6 in this:
http://www.computing.net/hardware/wwwboard/forum/41007.html

I'm not sure how that relates to current cpu's, but the L2 limit of how much ram can be cached is still there.

Your response doesn't make any sense to me.

There are several things you can do.

Workaround - use just 1GB of ram, sell the other one - according to Kingston you don't need more than 1GB:
http://www.kingston.com/tools/assessor/winxp.asp

Rarely, the Auto settings in your bios may get the settings for your ram wrong. I doubt this is your problem because one 1GB module works fine.
Bios Setup - CPU PnP Setup - select something other than Auto for the cpu and ram speed - probably 533mhz, or 266mhz if 533mhz is not displayed for the cpu; 266mhz for the ram.

Email Kingston about your problem - I have found in the past that they do respond within a few days.
Technical Support Problem Report
http://www.kingston.com/support/newtechsupportform.asp
..........

If you don't "get" how the L2 cache size determines whether all or part of your ram is cached depending on how much ram you have installed on the board,
See Response 6 in this and go to the links I pointed to and read them:
http://www.computing.net/hardware/wwwboard/forum/41007.html

Further info, so far:

Go here:
http://www.kingston.com/tools/

Utilimate Memory Guide
This document was made in 2001. DDR ram is only briefly mentioned; DDR2 ram is not mentioned at all. Installation of DDR ram is the same as for 184 pin RIMM modules.

Pages 36, 37 of the pdf - cache memory, how cache memory works.
....

DDR Ram White Paper - detailed DDR ram information.
...........................................

See: ValueRam - ValueRAM DDR2 FAQ - explains what it is, and the differences between it and DDR ram, etc.
http://www.kingston.com/literature/default.asp
.....................