This link will provide you with a lot of accurate information, benchmarks and testing of the 440. On the whole it's not a bad card, but it will definitely not run the latest games at any acceptable frame rates.
The overall conclusion is that you should at least try to get the GTS 450, instead of the 440, but with a better PSU as well, your actual is not very powerful and it will not be quite enough for a more demanding setup.
These are the minimum specs for Assassin's Creed:
Processor: Dual core processor 2.6 GHz Intel Pentium D or AMD Athlon 64 X2 3800+
RAM: 2 GB
Video Card: 256 MB DirectX 10.0-compliant video card or DirectX 9.0-compliant card with Shader Model 3.0 or higher
Sound Card: DirectX 9.0 or 10.0 compliant sound card
HDD Space: 12GB
DirectX Version: DirectX 10.0
Assassin's Creed 2 minimum requirements:
OS: Windows XP (32-64 bits) / Windows Vista (32-64 bits)/ Windows 7 (32-64 bits)
Processor: Intel Core 2 Duo 1.8 GHZ or AMD Athlon X2 64 2.4GHZ
RAM: 1.5 GB Windows XP / 2 GB Windows Vista – Windows 7
Video Card: 256 MB DirectX 9.0–compliant card with Shader Model 3.0 or higher (see supported list)
Sound Card: DirectX 9.0 –compliant sound card
DirectX Version: DirectX 9.0
DVD-ROM: DVD-ROM dual-layer drive
Hard Drive Space: 8 GB
Peripherals Supported: Keyboard, mouse, optional controller
Assassin's Creed Brotherhood minimum specs:
OS: Windows XP, Vista or Windows 7
CPU: Intel Core 2 Duo 1.8 GHZ or AMD Athlon X2 64 2.4GHZ
RAM: 1.5 GB XP (or 2 GB for Vista/7)
HDD: 8 GB free disk space
Graphics: 256 MB Graphics Memory with Shader Model 3.0
Sound Card: DirectX 9 Compatible
DirectX: Version 9.0c
You will have to bear in mind that all these are minimum requirements, you will run the games but you will miss out on some very nice looking effects, with lowered graphics.
What I would recommend, and not very expensive (in the range of $100-130) is the 5770 from ATI; I have played these games and the latest ones actually, at 1920x1080 resolution without problems (maybe lowered graphics and details a bit in BF3 and Metro 2033 which are so very demanding games). But you need to take into account the rest of my setup.
Still, in my own opinion, that would be one of the best cards for that price range, and I recommend it. I am not taking any sides here, ATI or Nvidia (I've owned both types of cards at one time or another), but I'd rather speak from own experience.