What would be the ideal compatables in ddr ram and mb/gb Video Card(s)..and how far can I get away with upgrades? What would be the top DDR & video Card upgrade for this system?

So far, I'm on eBay looking for upgrades! but not quite sure what to get for this desktop.

DESKTOP

Windows Vista Ultimate Edition (Build 6000) 32 bit operating system

System Specification

Memory (ram): 1021 MB CPU info: Genuine Intel(R) CPU 2140 @1.60GHZ 1.60 Ghz

CPU Chip: 2 x Pentium II

CPU Speed: 1596.2 MHz

Display Adapters: ATI Radeon HD 2400 PRO| RDPDD Chained DD | RDP Encoder Mirror Driver

Manufacturer: *Intel Corp.

Motherboard: *Intel Corporation D946GZIS

MEMORY

bank:

CHANN A DIMM 0
CHANN B DIMM 0

device: J6H1 J6J1

data width: 64

capacity: 536870912

speed: 533

DISPLAY

ATI Radeon HD 2400 PRO /

/

-- PS. Guitar plugged into mic's rear jack input..I can see the meter off the sound card working BUT NO SOUND. everything else with sounds on this computer works..except the recording mic. I also tried the front pannel mic input.nothing..any suggestions?

Thank You in advance