Advice to buy new RAM sticks

[XSI]

I want to add 1 GB of memory.

Current Specs:
AMD Athlon 64 3500+ Processor
Fujitsu SCALEO Pa 2550 Motherboard
2 x 512MB DDR2 533
Windows XP PRO SP2

According to you, what should I add another 2 x 512mb or should I go for 2 x 1 GB?

[Fryderyk]

Just check the timings of your current RAM with the help of cpu-z. I advise you to spend money in 2 x 1GB. The DDR2 market is really on and at reasonable prices at the moment.

[Squibbit]

-Go to Start -> Run and type "msconfig" -> Startup Tab. Just uncheck or disable those things that you do not require.
-Administrative Tools -> Services, find out what you can disable,
-Check your Startup shortcuts, see Start menu, Program, Start and turn off everything that is unnecessary.
-Clean your hard drive. Use defragmenter.
-What did you like antivirus and firewall? If you are using Norton then remove it as soon as possible.

This will give you a boost to speed up your computer. Afterwards you can consider adding the ram.

[XSI]

@ Squibbit
I have already done all that stuff. And I am using Windows firewall and my antivirus is Avast.

The trick is that I am super multitasker. So I think I really need to go for 2 x 1GB of RAM, it seems essential and it is better. The question is what is compatible with my motherboard.

[Squibbit]

For services, there are some who are logical, the kind of thing smart card, if not worry, you disabled. For the rest, Google "windows service" and look at the docs listed over there.