Looks like the aggressive DRM has led to this big price drop on the PC version of Assassins Creed 2.
PC Specifications for playing:
Supported OS: Windows XP / Vista (only)
Processor: Dual core processor 2.6 GHz Intel Pentium D or AMD Athlon 64 X2 3800+ (Intel Core 2 Duo 2.2 GHz or AMD Athlon 64 X2 4400+ or better recommended)
RAM: 2 GB (3 GB recommended)
Video Card: 256 MB DirectX 10.0compliant video card or DirectX 9.0compliant card with Shader Model 3.0 or higher (512 MB video card recommended) (see supported list)*
Sound Card: DirectX 9.0 or 10.0 compliant sound card (5.1 sound card recommended)
DirectX Version: DirectX 10.0 libraries (included on disc)
DVD-ROM: DVD-ROM dual-layer drive
Hard Drive Space: 12 GB
Peripherals Supported: Keyboard, mouse, optional controller (Xbox 360 Controller for Windows recommended)
*Supported Video Cards at Time of Release:
ATI RADEON X1300-1950 / HD 2000 / 3000 series
NVIDIA GeForce 6600-6800 / 7 / 8 / 9 series
As mentioned above, this game uses very aggressive DRM. You need to be connected to the Internet at ALL times to play. If your connection drops for a second, the game will freeze until it's back again. In practice I imagine this doesn't happen but worth bearing in mind. All saves are stored online as well. That means you can play on any internet connected machine (no DVD needed once installed) but also means that you can't play offline at all.
Worth bearing in mind but a good price for the higher quality PC release of AC2.