Mobo fried - Upgrading

mobo fried on one of my friends PCs. told them to just upgrade the processor, mobo, and ram instead of getting a new computer

it is an alienware, but figured just start making it custom than deal with them

AURORA ALIENWARE ATX DESKTOP CHASSIS
ASUS A8N-SLI N-FORCE 4 SLI REV.1.02 MB
ATHLON 64 3500 E 512KB CACHE 939-PIN
PDP 512MB DDR PC3200LL
LITE-ON 16X DVD-ROM REV.4
SAMSUNG SPINPOINT 160GB SATA 3G NCQ
ASUS A8N-SLI REALTEK ALC850 ON-BOARD AUDIO
EVGA NVIDIA GEFORCE 7600 GT 256MB PCIE
ALIENGUISE INVADER
VANTEC 92MM STEALTH CHASSIS FAN
VANTEC 120MM STEALTH CHASSIS FAN
ALIENWARE ACOUSTIC PADDING FOR MID-TOWER
AMD FX57 DUAL CORE HSF CL-
650 WATT ATX2.0 24P PSU W/ ACTIVE PFC
GFX CK03-1225 DUAL SLOT CARD KEEPER


they have a different video card (asus 9800gtx+) that will be used in the new system. price range is between 400-600 for ram, cpu, and mobo. they play some games sc2, warhammer, etc (nothing that requires sli/crossfire. other than that the computer is used for web browsing and other daily activities nothing special.

any help would be good. I was thinking an i5, but wasn't sure which motherboard. also not sure if an AMD chip would suffice and can actually save money. appreicate any input.