I know it's a dumb question.. so would someone just help a newbie out here?

Control Panel --> System
For windows XP x86 it willbe only Professional (version 2002)
For win xp x64 it will show x64 Professional (Version 2003 )
That's it !!!!!

or even easier, when u boot up windows, does it say x64 edition ?

I believe the x64 build reports "Windows xp 64-Bit Edition" at the bootscreen. Since Windows XP v64 is the missing link when finding Windows Server 2003 Web Edition, I'm pretty sure we won't have to worry about any more flavors of Windows XP.

On boot it says "Windows XP x64 Edition" like XP Home and Pro did prior to SP2.... So yeah... Otherwise go to Run>'winver'... Otherwise, Windows Key+Pause.....

Is Win XP Pro a 64 bit OS ??. What abt win Home also ??

XP Pro has a 64 bit version, there is no 64 bit home.