If they are LimeWire folders, why do you want to prevent access?
Why not just move them elsewhere?
What OS are you running? If W2K, you can encrypt them or deny access to anyone but yourself.
If W9X, you can download a file encryption program to encrypt your files from tucows or Ziff Davis, etc.
Once you share anything you leave a hole for invaders. Your best bet is to use 1PC just for the internet and to put nothing personal on it. With the price of PC's these days, you can put together a machine for less than $300 for cruising the net. You don't even need a second keybd, monitor, and mouse; just use a KVM switch. Or, if you can't afford two machines, you can buy a second hard drive for next to nothing; install an operating system on it and have one disk for personal use and one for the internet. You just have to switch the cable betweent the two and there are add-ons available that will let you do that at the flick of a switch without having to unplug and swap the cable physically every time you want to switch.