I'm pretty sure I'm running bitcoin 0.6.0rc2. But i guess rc1 broke my bitcoin db somehow.
Im currently testing on another machine, where I switched directly from 0.5.2 to 0.6.0rc2 at block 167000. But still have to download 1000 blocks. If this works ill just copy the database to the other machine.
1) You can use 0.5 bitcoind.
2) If you used the windows installer you almost certainly are not running 0.6.0 rc2. It will say it installed but it doesn't overwrite everything from 0.6.0 rc1.
3) For p2pool I recommend using a bitcoind instance w/ a "blank wallet" and manually setting the payment address. That way a bad wallet simply means delete wallet.dat and relaunch bitcoind to create a new one.
4) For custom windows installs the zip file is preferable. You can drop it in a custom folder, delete the GUI bitcoin, and set data directory to the same folder. Upgrading or replacing simple means deleting the folder.