Advice on new system, please

[Rob 240]

Hi all.
this is what i am running at the moment:
Asus p4p800-x
Pentium 4 3Ghz prescott (ht)
cooler master igreen 430w
cpu/fan: asus Arctic Square
Western digital 250G sata 2 7200 16mb
kingston 2G ddr1 pc3200
Ati x1650pro 512mb ddr2
win xp sp3.
im giving it family.
The two things i plan on keeping are the cpu fan and the HD. the cpu fan is only about 2 mnths old. (the zalman died after 13mnths) Great, one mnth after the garantie finished.
the pieces i want to put together are the folowing:

intel core 2 duo E8400 3ghz,/E8500 3.16ghz.
Motherboard:
Asrock 4Core1600P35-WiFi+,/ asrock P45R2000,/ Gigabyte EP35-DS3P/DS4.
Power supply:
Corsair-TX650 Watts (CMPSU-650TX) - ATX12V v2.2 - SLI, Certification 80Plus.
memory:
Crucial Ballistix 2 Go DDR2 wich type ?

i need a graphics card that is direct x9, do i not ? a dx10 card will not work with my xp sp3 will it ?
graphics:
GeForce 7600GS - 512DDR2, /ASUS GeForce 7300GT Silent - 512DDR2,/ GeForce 8600GTS - 512 Mo DDR3.( i think these are all dx9)

And i want to put it in a Raidmax (sagitta) case. 2 12cm fans, one 8cm. very basic, front(bottom) back(top) side (top left) .

wich motherboard would be best?
wich proc?
is the power supply good enough?
wich memory frecuency to go with the proc? should i pick another make? 2G should be enough, no ?

Will this system (if it works out) be alot more performent than the system i have at the moment, will i see the difference?
thank you for your time
Rob.

[Rob 240]

Asus P5K-E/WIFI-AP
intel E8400 3ghz duo
saphire HD3650 512ddr2 direct x 10 PCI-Express 2.0
OCZ StealthXStream 500 Watts
2 x CRUCIAL DDR2 PC2-8500 1 Go 1066 MHz Ballistix
1 x samsung DVD 20X LightScribe SuperMulti SH-S202N (ide)
1 x samsung DVD 22X SuperMulti SH-S223F (sata)
asus silent square
WD 250G 7200 16mb
xp sp3
2 x 12cm fan, 1 x 8 cm.
raidmax sagitta case. ( fans changed)
pc stable , hard drive change went very well, no bios problem's at all.