A7N8X Deluxe based system running problems, advice needed

Hello!

My PC is having something of a 'stuttering' problem during 3D games.
In Planetside in particular this is especially awful. This isn't
internet latency I'm talking about, it's definately the process of the
game itself and it has manifested itself on all 3D games I've tried
(online and offline) to some greater or lesser extent. Adjusting the
graphics settings makes no difference so that lends itself to suggest
it's latency, but this happens with offline games too.

Oh, and mit takes aaaaages to shutdown too (running XP home). Can take
upwards of 60 seconds before it shuts down/restarts

My machine specs are;

Asus A7N8X Deluxe Motherboard
512mb DDR333 RAM (manufacture unknown)
Maxtor 6Y120P0 120gb 7200rps 8mb cache HDD
AMD 2700+ processor
Sapphire Radeon 9700 (non-pro)

I'm currently running the latest bios version (1007 final) on my MB,
have the latest Radeon Catalyst card drivers, have the latest Nvidia
NForce 2
chipset drivers for my MB. Using the ID controller than came with the
latest set of NForce 2 drivers, too.

These problems have preceeded all of my driver updates and they didn't
resolve them.

I've heard this can be a common problem (stuttering) with this Asus
board and was wondering if anyone has any advice or experience is
dealing with this?
Also wondering if I've accidently botched a setting somewhere or
installed
some duff program.

I did have my hard-drive replaced recently under warranty as I really
thought it was that causing the problems, but the performance seems
exactly the same.

Ran SiSoft Sandra and it rated my HDD about 3500 and this didn't look
a particularly good score compared to the comparative scores given.
Although it did advise me to disable silent mode on my HDD to increase
speed a little, which I have no idea how to do or if it's worth doing.

I would be eternally gratefully for ANY and ALL tweaking advice that
would help me get my computer to run as it should do!

Thanks