If using Windows 7, look into their "Backup and Restore" panel.
Use Windows 7's built in System Image tool and create a backup of your Windows 7 install to an external hard disk. Install your new hard drive, boot from your Windows 7 DVD and choose to restore a system image and point to the location where the System Image is backed up.
Edit: Since you don't have an external hard drive:
And when restoring, just use that network location again.
Using a wired connection would make it a lot faster, however if you're patient and trust a wireless connection for a complete backup, go ahead
. ETHERNET THAT BITCH!