HELP! I am getting this window for the past couple of days when I start up my pc:

C:\WINNT\system32\atipdsxx.exe
16 bit MS-DOS Subsystem
C:\WINNT\system32\atipdsxx.exe
The NTVDM CPU has encountered an illegal instruction.
CS:053a IP:0112 OP:8f 90 8f 94 96 Choose close to terminate the application.

Have you added any programs in the last few days? As the message says, this is being generated from a DOS program starting up when your computer does.

There are lots of programs that will identity and allow you disable any programs starting automatically. I prefer Spybot Search and Destroy ('Tools' on the menu).