Quale ram e dove acquistarla?

[ARMADUK]

Ciao ho un desktop cosi' composto:

Motherboard:
QuadCore Processor Type AMD Phenom II X4 940 Black Edition, 3000 MHz (15 x 200)
Name motherboard DFI LANParty DK-790FXB M2RS (H) (3 PCI, 3 PCI-E x16, 4 DDR2 DIMM, Audio, Gigabit LAN)
Motherboard chipset AMD 790FX, AMD K10
System Memory 3328 MB (DDR2-800 DDR2 SDRAM)
DIMM1: Corsair XMS2 DHX 2GB DDR2-800 DDR2 SDRAM CM2X2048-6400C5DHX (5-5-5-18 @ 400 MHz) (4-4-4-13 @ 270 MHz)
DIMM2: Corsair XMS2 DHX 2GB DDR2-800 DDR2 SDRAM CM2X2048-6400C5DHX (5-5-5-18 @ 400 MHz) (4-4-4-13 @ 270 MHz)
BIOS Type Award (12/26/0
Communication Port Communications Port (COM1)

Video card:
Video adapter ATI Radeon HD 4800 Series (Microsoft Corporation WDDM 1.1) (1024 MB)
Video adapter ATI Radeon HD 4800 Series (Microsoft Corporation WDDM 1.1) (1024 MB)
3D accelerator ATI Radeon HD 4850 (RV770)
Screen Monitor Generic PnP [NODB] (U7A0943017756)

Multimedia:
Audio device ATI Radeon HDMI @ ATI RV770 / 790 - High Definition Audio Controller
Audio device Realtek ALC889A @ ATI SB750 - High Definition Audio Controller

Disk Drive SAMSUNG SSD 250 Giga
Disk Drive SAMSUNG HD501LJ ATA Device (500 GB, 7200 RPM, SATA-II)
Disk Drive SAMSUNG HD501LJ ATA Device (500 GB, 7200 RPM, SATA-II)
Disk drives WESTERN DIGITAL T 1, 7200 RPM, SATA-II
Optical drive HL-DT-ST DVDRAM GH22NS40 ATA Device (DVD + R9: 16x, DVD-R9: 12x, DVD + RW: 22x / 8x, DVD-RW: 22x / 6x, DVD-RAM: 12x, DVD-ROM: 16x, CD: 48x / 32x / 48x DVD + RW / DVD-RW / DVD-RAM)

Se volessi aumentare la ram che modello dovrei acquistare e dove a buon prezzo? Dovrei poi necessariamente passare a Window 7 a 64 bit giusto?

Grazie

Ciao

[Cobain]

ciao ho un kit performante e selezionato di dd2 crucial ballistix se ti puo interessare sono il meglio su standard ddr2.