Hi ,
XP use to run a Bitcoin 3 Version from late december 2010 .
current Version 0.8.3
starts synchronising the pop up "failed to write undo"
client closes
thanks
1. open windows explorer
2. type "%appdata%\bitcoin" into address bar
3. delete everything EXCEPT for wallet.dat and bitcoin.conf (if it exists)
4. start bitcoin-qt 0.8.3
if it doesn't work, upgrade to windows 7