Glad to be of help, Dragon Wench.
1. Either of those Samsung monitors will do very well. The thing I like about the 20" is that you can get higher resolutions. I usually go to NewEgg.com and read the customer reviews.
2. I agree with your friend in that the default processor will do you very well, though my question to you is how often do you upgrade?
3. I fully agree with him about the price to performance ratio on the Video Card. How many software applications, let alone games, really utilize even 640mbs of memory? IMO, 768 is overkill. There are other companies that make good 8800 cards that are not overclocked.
4. Here is a great link about your motherboard. If you want, just skip to the conclusion. I think you will be pleased.
[H] Enthusiast - ASUS P5K Deluxe WiFi-AP Edition
5. Memory: Crucial, Kingston, Corsair, Gskill. Google your motherboard and find Asus' product page on your particular motherboard. They usually have listed on the left side recommended memory. Stick with that memory.