I once installed Riven on my windows xp system and it ran perfectly fine. Now I want to install it again, but I got this error message: C:\windows\system32\autoexec.nt. The system file is not suitable for MS-DOS and Microsoft Windows apllications

I have this system:
Windows XP Professional
Celeron(R) CPU 1.50GHz
224 MB RAM-memory

Now I tried to run the game on an older computer, but also with Windows XP Professional. On this machine the game runs fine. The system is:
AMD Duron processor
64 MB RAM-memory

I don't understand why it does run on the older machine with Windows XP, and why it ran before on the newer pc and now it doesn't. Can someone help me out?