If this is old news to everyone else, I'm sorry. I just realized this the other day and wanted to share.
If you go to the main page of the group,
http://community.livejournal.com/house_wilson/profile, and click on the magnifying glass, you get to search the community. That part's probably old news, but also you have an option after that for an advanced search. You can search by journal or you can search by friends. So if you were pretty sure the fic you are looking for was by someone on your flist, you can enter your journal and it will search their journals too. Very useful when your search terms aren't terribly specific.
Like the fic someone was looking for below about House and Wilson on the balcony drinking beer and looking at stars while House is zoned on Vicodin- I went to advanced search and looked for "house wilson balcony beer Vicodin stars". Granted, I found a lot of other stuff, too but there it was!
Also, you can just go here for the search engine-
http://www.ljseek.com/. If you're like me though, you can get there faster from the main page than by finding or typing that link.
Another thing that's helpful is searching a journal by entries. Say you're looking for a fic that you know read at house_wilson and you can't remember the tile, but you feel sure you'd know it if you saw it, you can pull up the calendar and browse by post titles. You'll also see who posted it. Much easier than scrolling through the comm one page at a time.
Anyway, didn't mean to pontificate. Hopefully this will be helpful to someone. :-)