Hi just joined, only moved over from PC in March 2009 (I realize now, it was a ridiculous mistake waiting this long)

I've upgraded the HDD, Installed Leopard, connected my Lacie Firewire 800 External Drive to install the previous files/settings from Time Machine, All went fine until the password shook around saying it was incorrect. Its without a doubt the right password, no question about it. Tried another keyboard incase it was faulty, it wasn't. Had to put old HDD back in, works fine but I'm concerned, if this one fails, are my hourly backups rendered useless as I cant access them on a new install??
Please help, Im still a little out of my comfort zone as new to Mac.