I think the appointment only applies to senators. Though he'd have to resign before a certain date or the seat would just be left open until the 2012 election came then, presumably because not enough time would be left for them to do an election or for the rep to do much before the coming election after that.
Republicans like those kid of elections. We went through one in my district when I lived in San Diego when we had to replace Duke Cunningham some years back. Hopefully though, with our district's makeup, we'd still get a Democrat winning, though one never knows. The gentleman that ran in the primaries against Wu, David Robinson, seemed to be a decent enough guy, and might be able to do well in a special election. I just sensed he didn't have anough different policies from Wu to warrant voting against Wu then.
I also heard rumors from the Dem running against Duncan Hunter in a neighboring San Diego district (the older one) some years back that he was being investigated and potentially going to be indicted, but that the prosecutor's office was holding off because the Republicans would rather have had him replaced in a special election later instead of having him put out of action or under indictment before the election, having been successful in getting in Brian Bilbray in a special election to replace Duke Cunningham. Then of course right after the election, Carol Lam of that local prosecutor's office got fired (in one of Bush's famous firings) and had her hands full just to get a number of other high profile indictments filed before she left office near Valentine's day (Dusty Foggo, Brent Wilkes, John T. Michaels, and Thomas Kontogiannis), so Duncan Hunter got "off the hook" and probably google bombed himself from getting further scrutiny by running for the Republican nomination for president after that (which everyone knew was a losing battle).
Thankfully Oregon doesn't have any voting machines int this state and has vote by mail instead to avoid the games that the Republicans played in swearing in Bilbray before all of the votes were counted in an election that there was going to be a challenge to do a recount, but wasn't allowed because of that premature swearing in, which a local judge claimed he had no jurisdiction over to counteract.
http://electiondefensealliance.org/8_24_09_fight_back_against_election_nullification_in_san_diegoMuch like Scott Walker, the Republicans would pull out all of the funky stops to grab a seat with dirty tricks like this, especially now that Boner is Speaker of the House much like Hastert was then.
Here's some other speculation who might replace Wu if he resigned that seem a tad right wing leaning, though there's notes here that he's already filed to run in 2012...
http://oregoncatalyst.com/7635-who-will-fill-wus-shoes.htmlJust earlier today, it would appear that Wu is still saying he will not resign...
http://www.katu.com/news/116981663.html