Flyjac said:
Well that sucks for me then, having bought a game I thought I could play

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Are there even any "official" requirements? I thought Steam would be reliable but it seems like that is not the case.
Yes, official "minimum" and "recommended" requirements have been out since before release.
Minimum System Requirements
OS: Windows XP SP2 / Windows Vista SP2 / Windows 7 (32/64-bit)
Processor: Intel Core 2 Duo 2.2 Ghz or AMD Athlon 64 X2 5000+
Memory: 1 GB Windows XP / 2 GB Windows Vista and Windows 7
Video Card: 512 MB RAM, supporting Pixel Shader 3.0 (NVIDIA GeForce 8800)
Recommended System Requirements
OS: Windows XP SP2 / Windows Vista SP2 / Windows 7 (32/64-bit)
Processor: Intel Core 2 Quad or AMD Phenom X4
Memory: 3 GB Windows XP / 4 GB Windows Vista and Windows 7
Video Card: 1 GB RAM, supporting Pixel Shader 3.0 (NVIDIA GeForce GTX 260)
Additional Requirements
Sound Card: compatible with DirectX 9.0c
HDD: 16 GB of disc space
Disc Drive: DVD x8, compatible with DVD9
Installation requires administrator access
The problem is, few actually understand how to relate those requirements to the confusing model numbers that graphics card makers use.
A good enough oversimplification is to look at the _second_ digit of the card model number.
nVidia 8-level (8800, 9800, 280, 285, 480, 580, 680, 780) cards are the most powerful in each generation (except for 9-level cards, which are duals, and Titan). More recent cards down to 6-level (260, 460, 560, 660, 760) are still powerful enough to qualify as "recommended". More recent 5-level cards (250, 450, 550, 650) are above "minimum".
AMD 8-level and 9-level (48xx, 58xx, 69xx, 79xx) are the most powerful in each generation. 7-level (47xx, 57xx, 67xx, 77xx) are still powerful enough to qualify as "recommended". 6-level (46xx, 56xx, 66xx) are below "minimum".
Many below-minimum cards are still playable, when you trade eye candy for frame rate.
Older nVidia cards with 8 ROP's (8600, 9500, GT 220, GT 240) Sadly, nVidia dropped the 8-ROP designs from newer low-end cards; thus cards like the 430 and 530 have only 4 ROP's and are frequently unplayable.
AMD cards with 8 ROP's (4670, 5570, 5670, 6570, 6670, 7570, 7670) AMD continues to use the 8-ROP designs in recent series, meaning AMD has the market to itself in low-priced cards that will actually run this game decently.