Patrick,
512MB is the least amount required for Windows XP, but for better performance (think of the other software you'll be using; web browser, e-mail, games and all the other toys you'd like to have), go for 1GB. 2GB is the max you can have safely with WinXP 32bit.
I have 2GB on my box, and with everything I normally run at the same time, I'm usually using 40 to 60% of the RAM available.
My best suggestion would be you to purchase another same brand/type 512MB module, and place it the correct slot per your motherboard specs. Most of today's MB have color coded memory slots, to make it easier.
Can you say "Hang time". At least you'll running a smoother PC, then waiting for the overflowed memory to be taken off your virtual memory (hard drive, Linux calls this space, /swap), to be written back to RAM and what Windows doesn't need to written back to virtual memory.
I've repaired stories about, "My computer freezes, takes to long, etc.", just by recommending they buy some more RAM. Then, if you want to 'blow your socks off', save $ to get the other 1GB, either one 1GB module or two 512MB modules.

Good Luck,
Tim
 -------------- Original message ----------------------
From: Patrick Macaspac <[log in to unmask]>
> Hello Jeffrey,
>    
>   I will be using Windows XP SP2.
>    
>   Thanks.
>    
>   PatrickM
> 
> J Ottie <[log in to unmask]> wrote:
>   Original Message -- 
> From: Patrick Macaspac
> Sent: Thursday, August 23, 2007 10:13 PM
> Subject: [PCBUILD] Your help is appreciated.
> 
> 
> Hi people of PCBUILD and members:
> 
> Is a single 512Mb (PC800 DDR2) memory module enough?
> 
> Patrick M.
> 
> 
> $$$
> 
> Hello Patrick,
> 
> What operating system will use be installing on your new PC?
> Windows? Linux? Unbuntu? Kubuntu?
> If Windows, which version??
> 
> Awaiting your reply. I am,
> 
> Very truly yours,
> Jeffrey Ottie
> 
> 
> eom
> 
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