Answers:
Reasonably safe and sound. Skype uses proprietary protocols and its encryption is strong, but VoIP use have exploded and the hackers are onto it. At this stage they give the impression of being to be focused on using Skype IM.
Recommendation, use a fully clad commercial antivirus and firewall. The weakest relation within the fasten is Windows, whether your using XP or Vista.
Today the risks are low, that will transfer.