How to install older windows without using dvd/cd

[carnageX]

It looks like COD4 was only made to run on XP or Vista, so that may be part of the problem. That said, if you don't have enough RAM to run both Windows and COD, that's going to cause lag issues.

CoD4 runs fine on Win7; I've even run it on Win8.1 just fine.

 

[C0RR0SIVE]

You do need a faster CPU and more RAM to be running 7... XP is a big no-no unless it's on an off-line isolated network all by it self. Consider upping to a dual core CPU with 2GB+ of RAM minimum.