What proggie are you trying to install z0z3k
l?
Roady is right, 16 bit installers are not natively supported in XP (a 32bit OS). They were designed for 16bit OS's like Windows 3.1.
You could try to put it Win95 compatability mode as Win95 has some 16bit compatability. Right click on the .exe and look for the compatability tab, put it in Win95, and try installing again. There's no guarantee it will work, but it is worth a try.