Upgrade Office purposes PC

I need to upgrade the 4 x old Celeron CPU PC to Core 2 Duo CPU. These are the settings I want to buy:

APPROXIMATE PURCHASE DATE: this week
BUDGET RANGE: cheaper enough, at least my user in the office happy

SYSTEM USAGE FROM MOST TO LEAST IMPORTANT: Accessing Email from Outlook, Microsoft Word and Excel, surfing internet, accessing PDF, MYOB, occasionally watch movies

PARTS NOT REQUIRED: keyboard, mouse, monitor, speakers, Windows XP Professional 32 bit, Office 2003 / 2007 (can use license from previous PC)

PREFERRED WEBSITE(S) FOR PARTS: www.msy.com.au, www.cpl.net.au
COUNTRY OF ORIGIN: Australia

PARTS PREFERENCES:
- I'd prefer use Intel core 2 duo, as they seems have larger Cache memory (hopefully this might gives better user experience); but if AMD gives same result with Intel, I'm more than welcome to get better overview from you guys

OVERCLOCKING: No
SLI OR CROSSFIRE: No

MONITOR RESOLUTION: 1024x768

ADDITIONAL COMMENTS:
- Need to have fast computer for office usage, most of user don't like to wait for any slow computer processes (impatient user )
- Do I need to buy separate CPU fan cooler & heatsink?, I believe Core 2 DUO by default comes with fan cooler and heatsink, right?

Parts:
Ps: I will use newegg site to gives detail on the parts, as www.msy.com.au and www.cpl.net.au only give price list in PDF format

- Processor: Intel Core 2 Duo 2.93Ghz E7500
- Motherboard: Asus P5QPL-AM with built-in video card
- Memory: Kingston 2GB (2x1GB) - 800 PC 6400
- Casing: Coolermaster Elite RC335
- Hard Drive: 320GB Seagate SATA

Thanks heaps