When you browse the web, Skype will locate phone numbers and offer to let you call the phones through Skype. You have two options to disable this:
1) Uninstall "Skype Toolbar" from Add/Remove Programs.
2) In Skype, go to Tools > Options > Advanced and uncheck the boxes "Use Skype to call callto: links on the web" and "Automatically start Extras".
I recommend just getting rid of the toolbar, which often are culprits when web browsers crash.