It's not just you getting the exe files in your searches. It's been discussed on this forum before. I suggest yo go to your filters (LW menu-Tools-Options-Filters / for MacOS: LW Prefs/Filters) & enter the keyword .exe & press Apply. This should eradicate these unwanted items from your search results. There's a no. of threads about related subjects, one is : Quality of Content on the Network: (the 6th post on the page) http://www.gnutellaforums.com/showth...&pagenumber=12
& see the adjoining link. I think I saw it mentioned somewhere that these items are autoreleased (so to speak) by certain parties that detect searches along the Gnutella network. They will be related to the article in the above link.

Files like you mentioned that mysteriously reappear, definitely sound like spyware/viruses. Perhaps a pc person on this forum can give you a decent answer about how to rid of them. In the meantime see: http://www.gnutellaforums.com/showth...threadid=26605
http://www.gnutellaforums.com/showth...threadid=26903