If you can boot to XP PRO at startup and it's registry sees and runs all of the old programs you had installed then you can safely delete Home (or just disable the boot to Home option). Boot.ini file in the root directory has the boot up selection list.
If you boot to Pro and it does not have a complete registry (this is probably the case). You need to delete the new Pro install. (If it will let you, Windows resists uninstall.) Then go back and install it again but this time during the install watch for an option to install over or replace XP Home. It should ask you if you want to backup the old operating system so it can be restored. Say no to this since you have all your daat backed up. It creates a lot of clutter.
If this does not work Formatting is plan "B".
If you can not boot to PRO then you need to change the boot.ini setup. Edit it with notepad or search help and there is way to edit boot.ini using windows.
Note you can not install Home over a PRO install, windows refuses.
Startup options
-Open System in Control Panel.
-On the Advanced tab, under Startup and Recovery, click Settings.
-Under System startup, in the Default operating system list, click the operating system you want to start when you turn on or restart your computer.
-Select the Display list of operating systems for check box, and then type the number of seconds you want the list displayed before the default operating system starts automatically.