Hi Suky
That is a good point. I'm not sure what all the differences between the Home and Professional editions are. I know one of them is file security - the way you can change ownership and permissions of a folder or file. However, you can accomplish this in the Home edition by booting the PC in safety mode. There is a possibility that there will some minor compatibilty problems. The differences are explained here:
http://www.winsupersite.com/showcase/windowsxp_home_pro.aspI'd be inclined to wipe your hard drive (take the format option) and start again from scratch. Your main problem is that you need to register your copy of Windows XP so that it's WGA (Windows Genuine Advantage) Tool accepts that you have a legitimate copy of Windows. That way you will be entitled to all the updates - which includes IE7, firewall and the anti-spyware software. If you don't reinstall from scratch you may not get that option to register your copy of Windows. Having said that there is a Activate Windows option on:
Start->Programs->Accessories->System Tools.
It's a bit of a pain having to reinstall all your other applications (programs) and files and hardware (printer, scanner etc). If you have everything backed up its probably the best option.
downside
PS don't forget to backup your email.