I am having doubts about which components should I use so I could upgrade my current system which is pretty old, about 4 and a half years ago..
What are the Core 2 Duo cpu is all about?
which graphics adapter should I buy ( the best one for 190$ , even less )
I need a power supplier, and a 120GB harddisk..
also a motherboard and a processor ( that's why I mentioned the core 2 duo, or extreme, whatever it would be which is cheap )
Core 2 Duo - they are the fastest chips currently available. AMD is slightly behind in the dual-core market, and wayyyyyy behind in the quad-core market. Also, since Intel swapped from the older Netburst arch. to the new Core 2 Duo, you'd see massive performance gains in just about any application you use. (Assuming you have a P4 @ 2.4-3.0 Ghz, then just a cheap E4300 @ 1.8Ghz would net roughly 2-3x the performance in most games --This is just a rough estimate.)
Alright, here is a proposed build (Post your total budget if you can as well as your monitor size and / or resolution):
Budget: E2160 - This is one of the best, if not the best, budget chip you can currently buy. It will easily OC to the 3.0Ghz. ~$79-100
Recommended: E8400 - This is Intel's newest dual-core offering. It comes stock clocked at 3.0Ghz and should OC to 4.0Ghz on air w/o too much trouble. ~$180-200
Recommended: GA-P35-DS3L - A tried and true board from Gigabyte on the rock-solid P35 chipset. This is a great budget over-clocker, but if you need firewire or lots of SATA / eSATA, go with the GA-P35-DS4.
Best $ / Performance Card: The HD 3850 512MB. It will match or outperform the $200-300 8800GTS 320MB card while keeping the pricetag under $200. I've seen this card from $140-170 and it should play just about anything you throw at it.
Best Mid-range Performer: The 8800GT 512MB will come strongly recommended from anyone here. If you can afford a $200 card, this is definitely the way to go. It will play anything that is currently out and maxed settings (except Crysis, of course).
For a single graphics card, try a Corsair 520HX or 550VX. The HX is a modular PSU, meaning you can attach only what cables are needed. Both PSU's are top notch in my book
RAM: Check Newegg or NCIXUS for RAM. I'm pretty sure both had some $29.99 deals for 2GB of DDR2 800 (PC6400) RAM. Look for brands like: Patriot, OCZ, Crucial, or Corsair. Gskill and A-Data are also acceptable.