I accidentally deleted Bonjour from my computer, is there a way to re-add it?

I have a very old, Dell Windows XP computer, that frequently runs out of space on the.. hard drive?? I don't know anything about computers... But it recommended I delete some softwares that were rarely used; so I did. I actually didn't know what Bonjour was until a few days later I opened up Itunes and all my songs were missing! Is there any way to get them back? There were thousands upon thousands of songs!!