Jadariin , AMD Athlon 64 X2 is already available here in Philippines FYI but not many resellers have it. ^_^ Lets admit it that majority are order basis form. But when it comes to me, it will not be a problem. By the way Im from Philippines also as you can see in my icon ^_^
.. Its store is located at Manila. You can check their map if you wish to go there. The price is still high right now but as AMD drop their prices, except to get an Athlon 64 X2 3800+ for $159 (Php 8000+) ^_^ They dont have X2 in AM2 socket in the website but I called them last 2 days and they told me they have it in order basis form. I suggest getting Socket AM2 instead of 939 when you choose AMD Cpu for future upgradability.
Of course, many parts in your planned system will be changed. Like the RAM, you will be going to use 240-pin DDR2
instead of DDR 400 ones. And when choosing RAM, go with dual-channel. Top brand names like OCZ, Geil, Patriot and others have dual-channel kits that have RAMs in pairs for assurance of dual-channel performance. And check their latencies too. Try to find with CAS4 latencies. ^_^ Latest DDR2 RAM available here is only DDR2 533Mhz sad. But try to find and you might stumble on DDR2 800Mhz.
Regarding the motherboard, my best suggestion would be the MSI K9N Neo-F nForce 550 Chipset motherboard. I heard lots of good reviews on MSI and I prefer it over ASUS.
Let me have you a price jut-down of some parts.
AMD Athlon 64 X2 3800+ Php 17-18K (current price)expect it to go down after release of Core 2 Duo
MSI K9N Neo-F Php 4,800
2x 512MB (1GB Total) GEIL DDR2 533 Dual-Channel Kit Php 4,650
***EDIT*** Additional suggestions
Now since many says that most applications right now are made for single processors, choosing the X2 will be the future proof. But if you are more on a tight budget, I may have some alternative for you. Let's say you will choose single -core. Get socket AM2 as what Ive said.
AMD Athlon 64 3200+ Socket AM2 - Php 6,200
MSI K9N Neo-F Php 4,800
2x512MB GEIL DDR2 533Mhz Dual-Channel Kit Php 4,650
*Price above are from www.pcx.com.ph/catalog/
some other parts then spend the rest of your money on the gfx card. Just another suggestion when it comes to budget.
If you can't afford Core 2 Duo and need a brand new pc badly, then go X2. But if you can wait and save more money, go with Core 2 Duo.
Im gonna post some more links of sellers here when I have time. Got to review for exams ^_^