I agree with the idea of getting a new system. Especially if you want to play Oblivion.
Wanna go high-end and keep the system for a long time?
http://www.cyberpowerpc.com/system/cfga64x2.asp?v=d
Change the parts so that you have these. You can add anything else if you want to
$1455.00
CASE : HOT NEW! X-Discovery Mid-Tower Case 420W W/ WINDOW & LCD Temperature Display (Silver Color)
CPU : (939-pin) AMD Athlon™64 X2 3800+ Dual-Core CPU w/ HyperTransport Technology
MOTHERBOARD : (939-pin Socket) Gigabyte GA-K8NF-9 nForce4 Chipset MB w/ LAN, USB2.0, IEEE, & AUDIO
MEMORY : 2048 MB (1GBx2) PC3200 400MHz Dual Channel DDR MEMORY (Corsair Value Select)
VIDEO CARD : NEW !!! NVIDIA Geforce 7900 GT 256MB 16X PCI Express Video Card
VIDEO CARD 2 : NONE
LCD Monitor : NONE
HARD DRIVE : Gaming Hard Drive (10,000RPM SATA150) (SATA150 - Western Digital Raptor 150GB 10,000RPM 16MB Cache WD1500ADFD)
Hard Drive 2 : NONE
Optical Drive : (Special Price) LG GWA-4161 16X DVD±R/±RW + CD-R/RW DRIVE DUAL LAYER (BEIGE COLOR)
Optical Drive 2 : NONE
SOUND : HIGH DEFINITION ON-BOARD 7.1 AUDIO
You can change the video card to a 7900GTX or a X1900XT(X) if you want too.
Want a cheaper system?
http://www.cyberpowerpc.com/system/cfga64x2.asp?v=d (Yes it's the same link as before)
$1031.00
CASE : HOT NEW! X-Discovery Mid-Tower Case 420W W/ WINDOW & LCD Temperature Display (Silver Color)
CPU : (939-pin) AMD Athlon™64 X2 3800+ Dual-Core CPU w/ HyperTransport Technology
MOTHERBOARD : (939-pin Socket) Gigabyte GA-K8NF-9 nForce4 Chipset MB w/ LAN, USB2.0, IEEE, & AUDIO
MEMORY : 1024 MB (512MBx2) PC3200 400MHz Dual Channel DDR MEMORY (Corsair Value Select)
VIDEO CARD : NVIDIA Geforce 6800 GS 256MB 16X PCI EXPRESS VIDEO CARD
VIDEO CARD 2 : NONE
LCD Monitor : NONE
HARD DRIVE : Gaming Hard Drive (10,000RPM SATA150) (SATA150 - Western Digital Raptor 74GB 10,000RPM 8MB Cache WD740GD)
Hard Drive 2 : NONE
Optical Drive : (Special Price) LG GWA-4161 16X DVD±R/±RW + CD-R/RW DRIVE DUAL LAYER (BEIGE COLOR)
Optical Drive 2 : NONE
SOUND : HIGH DEFINITION ON-BOARD 7.1 AUDIO
I recommend the first if you got the money and the second if you want good performance for the price. The reason I recommend the 3800-X2 is because I've heard (and read) that Oblivion is multi-threaded and the games in the future will be multi-threaded too so your dual-core processor will take FULL advantage of that and accelerate your speed in those games. 1GB is recommended to play it on medium settings and a 6800GS is very good to play on medium settings too (I think) Also, for both of the systems, change the power supply to the **Cyberpowersystem recommended** 500W power supply
I think the minimum system specs for Oblivion is:
2.5GHz processor
512 MB memory
I think the ATi xpress 200 was the MINIMUM required to run Oblivion
I know you might think "Why do I have to get 1GB if 512MB is enough?" It's because the recommended system specs are:
3.0GHz CPU
1GB RAM
6600GT (My opinion)
And minimum system specs is their way of saying "You will NOT enjoy this" (Heard this on onrpg.com) So yeah, I think you should get at least the one that is $1,000 as that is a very good system.
And should you refuse to buy a new system, at least get these:
Power supply:
http://www.newegg.com/Product/Product.asp?Item=N82E16817103936
Video card:
http://www.newegg.com/Product/Product.asp?Item=N82E16814130272