In Limewire, go tools...options...sharing

Select the folders that you want to share. Other folders will NOT be shared.

I would also suggest that you have antivirus and firewall software (available free if you don't have them). Your firewall must be configured correctly in order to allow Limewire access to the internet.

The biggest risk with using Limewire, in my opinion, is downloading a virus. Read these threads...they'll help you avoid fake files that contain viruses:

How to filter porn & spam
Fake files showing up in search results
How to find music
What you should know about WMA files

Good Luck