Time Capsule help

Unfortunately, no. Time Machine backs up differently to a Time Capsule or Base Station attached HDD than it does to a USB/FireWire attached one. With the latter, it copies the files directly onto the hard drive. With the TC, it first creates an image of the backup, then copies that onto the drive itself. There's no way about it, you'll have to start the backup again. Use ethernet for your first backup to make it go faster than WiFi, but the incremental backups usually go quite fast (depending on how much has changed in one hour). Keep the old HDD around if you need those backups.