Hard drive and memory upgrades

[UK User]

I have a 4 year old MESH PC with an AMD64 3800 processor, Asus A8V Deluxe motherboard, 1Gb RAM running XP SP3. The 200Gb hard drive is nearly full. 2 questions:
1) I have added processor and graphics card heatsinks to keep the PC quiet very successfully. I now wish to add a second HD. Which of the 3 SATA drives available (Hitachi or Samsung) is quieter? These newer drives are likely to be faster than the old one so should I move the XP installation to the new drive and keep the old one for files? Is that straight forward?
2) From Tomshardware website it appears that 1.5Gb memory is about as good as performance gets for XP so I was going to add 2x256Mb sticks. Is there any point in going for 2x512Mb or higher?
Thanks.

[UK User]

Went for 2 sticks of 512Mb memory to make up to 2Gb. Has certainly improved speed of PC when running multiple software eg. email, browsing, Photoshop, and Skype. Certainly seems to be worth going above 1Gb. Incidently 512Mb is completely insufficient for XP to run well.

Of note installing 4 sticks of memory on the Asus A8V Deluxe board with a AMD 3800+ processor meant that the memory runs at 166Mb/s instead of 200Mb/s. This appears to be a known issue. Also the memory usage does not seem to get above 58% (1235Mb) so looks like total of 1.5Gb would have been enough.

As for the harddrive, appears the Spinpoint drives are well regarded.