Well...if you have a legal version of XP Pro, with license...you can do an upgrade.http://support.microsoft.com/kb/316639
But...I would not install XP on top of an existing Windows Me install..I would do a clean install.
A good summary of doing a clean install with an upgrade edition
of XP: Clean Install Procedure with Illustrative Screen Captures - http://www.theeldergeek.com/xp_home_install_-_graphic.htm
Installing XP Home and XP Pro...same procedures.
<<Will I have an extremely slow XP?>>
"Extremely slow" is not an exact phrase, so I can't answer that. But you can look at the minimums required and gather your own ideas. I've run XP Home with 384MB of RAM satisfactorily, but I'm easy to please
. And I didn't have a PIII processor.
You could always try running them side by side for a short time, a dual-boot situation.
Any system will normally respond faster...when there are fewer programs loaded/installed...and I think this might be more of a consideration than anything else.
<<Or should I run it as is. Just run it for kids to play and internet.>>
Well, I would never suggest to anyone to run Windows Me in 2009 (almost 2010), especially since any version of XP is already superseded by a newer version of Windows...make that 2 newer versions now. I can't think of any reason to pretend that I want to or can run Windows 9x/Me forever...I think that the alternatives presented by MS are better and security/support for Me has almost certainly stopped (I think).