After the last update, I had big flashing triangles, low FPS and bad shadows.

Intel Core 2 Duo T5500 (1.66 Ghz)
1 Gb RAM
NVIDIA GeForce Go 7400; 256 mb TurboCache

screenshot: 569001836334546949/unknown.png
Well that sure is one low end ..PC or.. Laptop..did you try and check your drivers for graphics by any chance? Perhaps update is required for those?

Or maybe try to tick off, Preferences > Games > Use graphics hardware for displaying maps(alpha-channels, anti-aliasing, etc.)

Try then?
This is something wrong with your graphics driver.