simple way: delete everything in %appdata%\bitcoin except for wallet.dat, then restart the client
faster way: use pywallet to manually remove the transaction from your wallet.dat, then run "bitcoin-qt.exe --rescan"
faster way: use pywallet to manually remove the transaction from your wallet.dat, then run "bitcoin-qt.exe --rescan"
For a faster solution without needing pywallet, you could just delete the most recent block database and chainstate files, then start bitcoin-qt with --rescan. It should still work, provided transactions aren't stored in wallet.dat after they've been broadcasted, which I'm not certain about. If they are, you'd have to either use pywallet or restore from a recent backup.
