Memory Installed 256 MB (1 x 256)
Maximum allowed 2 GB (2 x 1 GB) requires the replacement of the installed 256 MB DIMM
Speed supported PC2-4200 MB/sec
Type 240 pin, DDR2 SDRAM
DIMM slots Two
Open DIMM slots One
•160 GB SATA
16X DVD(+/-)R/RW RAM (+/-)R DL LightScribe drive
Modem 56K bps data/fax modem
Integrated High Definition audio
•Realtek ALC 883 chipset
•Supports up to 8 audio channels
•Dolby Pro Logic II compatible
Still need to know specifically what 4GB graphics card you're being offered (Model Number) and what power supply your system currently has installed (make and model number).
While the 4GB graphics card, assuming it's PCI-E (I don't know of any AGP or PCI 4GB cards), will physically fit into the PCI-E slot of your motherboard, we don't know if your system can support it. Also, based on the details you did provide, your system has far greater needs than a new graphics card.