No unless your playing the songs while you play MOH, just being on your harddrive will do nothing for the performance . You are doing the right thing by defraggin your system.
If you or your family surf the net a lot, Check your system for adware.
download the free program here:
http://www.lavasoftusa.com/
You will be surprised at home much of this spyware is on your system .This spyware can cause some problems with your system.
Run this on a regular basis ( after or before you defrag) and you should see a slight increase or just a more reliable system.
programs running in the background will do nothing for ping unless they are reporting back to there mothership, IE spyware.