Wait, don't delete or format anything yet.
What you did was a parallel install of XP Pro along side of XP Home. All you need to do is remove the entry for XP Home from boot.ini then delete it's directory structure on the hard drive (probably C:).
Press WinKey+R, type msconfig and press Enter
Click on the boot.ini tab. You will see a a default= and a couple entries under [operating systems].
Write down the path shown in the XP Home entry. It will look something like this:multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows XP Home Edition"
. The part you want is \WINDOWS
as that is the name of the directory (folder) in the root of the C: drive that contains all the XP Home files. XP Pro is probably \WINDOWS.0.
Now delete the line for XP Home, leave XP Professional. Select XP Pro and click on the "Set as default" button.
Click Apply then OK.
Right click on the Start button and select Explore. Expand (click on the + next to) the C: drive. Find the directory that matches the name you wrote down. Right click on it and select Delete. Click Yes when asked if it's okay. Click All when asked.
I know this sounds complicated but it really isn't. If you have any questions, post the data from your boot.ini here and I or someone else can help you determine what to delete in it and also what directory structure on your boot (C: most likely) drive.
You can also create a batch file of the following code and run it to look at or change the boot.ini file. Select it all, then right click and select copy. Open Notepad then click on Edit / Paste. Click on File then Save. Save the file to the Desktop as "xboot.bat" (enclose in double quotes). Now you can double click on xboot.bat on the Desktop to look at or change boot.ini or copy it's contents to post here.
@echo offc:cd \attrib -s -h -r boot.iniif exist bootbk3.ini goto is321if exist bootbk2.ini goto is21if exist bootbk1.ini goto is1:is321copy /y bootbk2.ini bootbk1.ini © /y bootbk3.ini bootbk2.ini © /y boot.ini bootbk3.inigoto edit:is21copy boot.ini bootbk3.inigoto edit:is1copy boot.ini bootbk2.inigoto edit:is0copy boot.ini bootbk1.ini:editx boot.ini & attrib +s +h +r boot.ini