After having looked at various online hardware retailers I still can't advise you very well on a card,
I played Oblivion on 1024*768 with a XFX Geforce 6800 256Mb once, and wasn't satisfied with how the game ran back then, but that's all about personal demands; lot's of eye-candy or barely playable.
As far as I can tell, between 40 and 60 quid you can't even find an ATI card that compares to a 6800. I might be wrong though, since I don't have experience with the newer Ati cards. Other Hardware Forums users should be able to shed more light on this then.
The closest you can get to that is a
Sapphire x1300 card with 256
DDR2 Memory for £62.69, the 6800 has
DDR3 memory and thus is much faster.
Maybe you could look on auction sites, like eBay and such for 2nd hand cards.
Here's the system requirements for The Elder Scrolls: Oblivion, lot's of cards seem supported, but under "Recommended" you'll find what you should be aiming for.
Recommended:
3 Ghz Intel Pentium 4 or equivalent processor
1 GB System RAM
ATI X800 series, NVIDIA GeForce 6800 series, or higher video card
Minimum System Requirements:
Windows XP, Windows 2000, Windows XP 64-bit
512MB System RAM
2 Ghz Intel Pentium 4 or equivalent processor
128MB Direct3D compatible video card
and DirectX 9.0 compatible driver;
8x DVD-ROM drive
4.6 GB free hard disk space
DirectX 9.0c (included)
DirectX 8.1 compatible sound card
Keyboard, Mouse
Supported Video Card Chipsets:
ATI X1900 series
ATI X1800 series
ATI X1600 series
ATI X1300 series
ATI X850 series
ATI x800 series
ATI x700 series
ATI x600 series
ATI Radeon 9800 series
ATI Radeon 9700 series
ATI Radeon 9600 series
ATI Radeon 9500 series
NVIDIA GeForce 7800 series
NVIDIA GeForce 6800 series
NVIDIA GeForce 6600 series
NVIDIA GeForce 6200 series
NVIDIA GeForce FX series
Anyway, good luck with your search.
Greetings,
Marcus