Upgrade Advice for my system

[Cheeseking25]

Hi. I am looking to upgrade my system to have better performance in today's more demanding games and in future games. First off let me say I DO NOT want to buy a new mobo or a new comp. These are my specs:

System Info
Model : Dell Dimension XPS 400/9150
Chassis Type : Tower
Operating System : Microsoft Windows XP Media Center Edition Professional Service Pack 2 (Build 2600)

Processor
Number Of Processors : 1 Hyper-Threading Enabled
Type : Intel Pentium D 820 2800 MHz (2.8 GHz)
Processors Bus Speed : 800 MHz

Motherboard
Manufacturer : Dell Inc.
Model : 0YC523 Rev. Not Available
CPU Slot/Socket Type : Socket 775 LGA
Chipset Vendor : Intel i945P/PL/G/GZ Rev. 00
Bios Manufacturer : Dell Inc.
Bios Version : A07
PSU: 375W

Graphics
Model : nVidia PCIE NVIDIA GeForce 6800 256MB @ 325 MHz
PCIE Speed : 16x
Monitor : Plug and Play Monitor

Storage
Hard Drive 1 : Maxtor 7 L250S0
Size : 238.42 GB

Memory
Total RAM Installed : 2048 MB @ 667 Mhz
Type : DDR2 Regular UDIMM PC4300
Used RAM Slots: 4 of 4


I am looking to upgrade my CPU and my GPU but if there are any other important upgrades it looks like I should make please tell me.

I'm not sure if I can upgrade my CPU to a Core 2 Duo. I have socket 775 LGA but I dont think my mobo is compatable. If I can't upgrade to Core 2 Duo should I upgrade to a higher Pentium D? Will a CPU upgrade help a lot?

For my GPU, I want to upgrade to something like a 8800GTS (GTX is too expensive). What are the differences (performance-wise) between the 320MB and 640MB 8800GTS's? Is it worth it to wait for the 9800GTS? Will a GPU upgrade help significantly more than a CPU upgrade?

I appreciate any help you can give me. I am also looking for a new monitor (20" widescreen-24" widescreen range). If there are any good monitors (preferably cheap) that you can reccomend please do. Thanks for any help you can give me.

[fade2black2004]

my dad has an intel PD 945 and it works pretty well for gaming and work related things, i would suggest that because i doubt your board supports core 2

for a video card an 8800GTS 320 is a very good card at a cheap price

BUT you PSU may not be able to handle that and from what ive seen Dell use proprietary PSU so you cant replace them

[ollithemagicbum]

want kind of heatsink are you gonna get? i heard pentium d's get knid of hot.