Blender crashes onr ender (vista)


I have some troubles with blender : sometimes (often…), when I hit F12 to render (it’s the same if I use the button in the UI), Blender crashes. It happens with all 2.5 (or more recent) versions of Blender, including Cycle versions, and it’s the same with complex or very basic scenes. It occurs more often when scenes or/and renders are big but not only.
I use a Q6600 cpu, with 4 Gb Ram, Vista family premium and I can’t remember any trouble like that with releases before 2.49 and no other graphic application I use shows the same issue (Carrara, Shade, Lightroom, photoshop,…)

Do you have any idea ?