My setup is somewhat unusual:
I have three primary partitions and one extended partition with Windows (C:) residing in a logical volume on it.
Apparently logical volumes can't be made bootable, so the boot files reside on the E: partition.
I used the awesome tool EasyBCD to set up the booting. Unfortunately you need a running Windows 7 / Vista to be able to use this tool. It seems to me you can't start it from Windows XP. This rules out using Bart's PE or similar tools which are based on Windows XP.
The recovery console you can use from Windows 7's installer (or rescue) disk does not allow you to execute EasyBCD either. ("Image subsystem not loaded" or a similar error occurs)
In my first attempt I have used the free EASEUS DIsk Copy tool (a bootable standalone CD copying entire partitions sector by sector) to copy my Windows partition to my new harddrive (using a big external HDD as intermediate).
Unfortunately the copied Windows on the new hard drive did not boot. The boot setup was missing. I started to search for more information on the net.
This is a very good guide if your setup is a bit easier, most probably you will be able to fix your booting problems with it (following the Nuke solution).
Unfortunately there were errors at different stages for me. I did not manage to make my Windows bootable again.
My theory is that it has been recreated as a logical volume on an extended partition – and logical volumes are not bootable (at least under Windows) (? correct me if I'm wrong).
Just use Windows' built-in tools.
Attach a big external harddrive to backup to
Control Panel -> Backup and Restore -> Create a system image
Select all partitions for backup
Burn the System Rescue CD it offers you to burn after the backup is complete
Power off the system
Change the harddrive
Boot with the CD you created (and the external harddrive attached)
Restore all partitions
Reboot into your Windows installation
This takes care of a lot of headaches … but it takes quite a while. Get a good book to read, or get busy cleaning up your room (as I have :-)
BTW, I also had Windows XP mode setup on another partition. Had I copied only one partition, Windows XP mode would have been broken. Just one example of problems you could run into trying to merge to a new drive manually.