I'd suggest macs are generally easier to connect than win pc's. So I'm a bit stumped if your pc laptop works fine at the same location. Do you connect them at the same time. That might be an issue.

If you have the mac firewall activated (not many people do) then see: http://www.limewire.com/english/content/firewalls.shtml

Try deleting LW's preferences found here:
/Users/your_username/Library/Preferences/LimeWire

If still not connecting then go to LW's prefs>Advanced>Firewalls & change from UPnP to manual port forward. Manual port forward instructions & sample image & 2 posts after that.

You could also try a different port no. for both the listening & forward port. eg: port 6342 or 5353 or something.