I would go with the Asus motherboard, and as far as memory, video cards, and hard drives, it all depends on what you need to get done.
With that processor and motherboard you already have a very nice start. If you have the money, I would suggest you go SATA (Serial ATA) on the hard drives. You can get two 80GB drives for around $160, which would give you 160GB, running in RAID 0 that would be very fast. You should get atleast 512MB PC3200 RAM. If you are only going to have 512MB of ram you need to go dual channel, which means you would have two sticks of PC3200 256MB. It's much faster. Imagine you are driving school busses to take children to school. Could you take more kids at once using 2 busses at the same time, or using one bus and making two trips?
The video card is up to you. Anything higher then the 9600 XT will do you fine for the next couple of years. The only big difference between the 9600's and the 9700+ is that once you hit the 9700 mark you go into 256 bit. The 9700, 9700 Pro, 9800, 9800 Pro, and 9800 XT are all 256 bit cards. While the 9600 XT is only 128 bit, that doesn't mean much as of right now. So you will be fine with the 9600 XT.
It all depends on how much you're willing to spend.