reinstall hal.dll file ?

This day, i was scanning my computer with AVG antivirus and surfing internet on the same computer. Suddenly the computer displayed a blue screen saying some message about the physical memory dump. It said to restart the computer if it was the first time i faced such a situation so i restarted the computer, and chose the last known good configuration. But the windows XP didn't start, instead it displayed: "Cannot load hal.dll file please reinstall the file.".....The computer also has vista installed. vista works fine but is slow compared to earlier.

I need to restore the XP to make it work again. What should i do? Suggest smthin.