Whats my next upgrade route

[Bar]

Afternoon all,

I currently have the following spec but I am looking to make the next round of upgrades. I am however unsure as to where to go.

Antec Nine Hundred Ultimate Gaming Case
AMD Athlon 64 X2 Dual Core 3800+ 2.00GHz (Socket AM2)
Zalman ZM500-HP Heatpipe Cooled 500W Modular PSU
Inno3D GeForce 9800 GTX 512Mb DDR3
Western Digital Caviar SE16 400GB 4000AAKS SATA-II 16MB Cache
Asrock ALiveSATA2-GLAN (Socket AM2) PCI-Express DDR2 Motherboard
Samsung SH-S203BEBN 20x20 DVD±RW Dual Layer Serial ATA ReWriter
Zalman CNPS9500-AM2 Aero Flower (Socket AM2/939/754) CPU Cooler
2 x GeIL 2GB (2x1GB) PC6400C4 800MHz Ultra Low Latency DDR2 Dual Channel Kit (GX22GB6400UDC
Windows XP 32bit Service Pack 3

So thats what I have now I need to know whats going to give me the best bang for buck. I am happy with all my current peripherals and have all the storage that I need.

My main focus on upgrading would be gfx, mobo, ram, cpu - I am just unsure as to what would be the best combination. I need an upgrade that will last me 18 months at least.

In terms of computer use it is primarily office based work, one large enterprise modelling tool and gaming. Main game is CS:S but I also like to play the C&C games.

To aid I have a number of budgets I am playing with so what would be my best bet if spending:

£200
£300
£400

Any help appreciated.

 

[Bar]

Thanks rifles and ginger - what mobo / cpu combination would be best.

Once I can justify it to myself what would be the next graphics card?

Finally - whats wrong with my current PSU or is 500W simply not enough these days?

edit - sorry my earlier post may not have been clear - I have 4Gb in 4 1Gb sticks - two lots of dual channel.

 

[Bar]

Thanks for the above. I have taken it into consideration and ended up with the following:

Intel Core 2 Quad Pro Q6600 "Energy Efficient SLACR 95W Edition" 2.40GHz (1066FSB) - OEM
Gigabyte GA-EP45T-UD3R Intel P45 (Socket 775) PCI-Express DDR3 Motherboard
Microsoft Windows Vista Home Premium SP1 64-Bit - OEM
GeIL 4GB (2x2GB) PC2-6400C4 800MHz Black Dragon EVO ONE DDR2 Dual Channel Kit (GE24GB800C4DC)
Western Digital Caviar Blue 160GB SATA-II 8MB Cache - OEM
Akasa SATA-2 60cm Silver Data Cable

Total Price for the above is £480.63 delivered and including.

Is there a cheaper mobo / cpu combination? I have gone for the harddrive to give me a clean seperate OS drive which I do not have at the moment.

I avoided the gigabyte EP43 earlier due to bad comments I have heard - is this common or a unique complaint?

Also what ADM cpu / mobo combination would be suitable? As I already have a solid AM2 cpu cooler. Really trying to keep total cost under £400.

Cheers