Intel Viiv Core 2 Duo or AMD Athlon 64 X2 Dual Core???

[londoner]

Hi, I hope this is the right place to ask this question, please forgive me if it's not. I want to buy a new Dell PC so I have been doing a bit of research (searching Google and this forum) but I'm still unsure what processor to go for. I don't know much about the inside of computers which is a bit ironic seeing as I make a living from the internet.
Any advice would be much appreciated.

I plan on having Windows Vista Home Premium as my operating system.



Here's the spec of the 2 Dell computers I've been looking at...


PC 1 (Dimension E521)

320GB (7200rpm) Serial ATA Hard Drive with 8MB DataBurst cache
2048MB Dual Channel DDR2 533MHz [2x1024] Memory
256MB ATI Radeon X1300 Pro graphics card
Network Card: Integrated 10/100 NIC

AMD Athlon 64 X2 Dual Core Processor 5000+

or pay an extra £82.25 for...

AMD Athlon 64 X2 Dual Core processor 5600+



PC 2 (Dimension 9200)

320GB Serial ATA RAID 0 Stripe [2x160GB 7200rpm drives with DataBurst cache]
2048MB Dual Channel DDR2 667MHz [4x512] Memory OR 2048MB Dual Channel DDR2 667MHz [2x1024] Memory (Both cost the same??)
256MB nVidia GeForce 7900GS graphics card
Network Card: Integrated Gigabit Ethernet 10/100/1000

Intel Viiv Core 2 Duo E6300 Processor (1.86GHz, 1066MHz, 2MB)

or pay an extra £52.87 for...

Intel Viiv Core 2 Duo E6400 Processor (2.13GHz, 1066MHz, 2MB)

or pay an extra £164.50 for...

Intel Viiv Core 2 Duo E6600 Processor (2.4GHz, 1066MHz, 4MB)



Both PCs are on this page... Find a Notebook, Desktop, Server, Printer, Software, Service, Monitor or TV at Dell. (Right of page)

Also, is 2x1024 better than 4x512?

I plan to buy one today as it's the last day of the current offers. I hope I have given enough details (and not too much). I would like to know your opinions on what system you think I should go for. Do you think it's worth going for the more expensive processors?

Many thanks in advance for your help and of course your time