Intel runs Windows natively
I don't know if I'm stating the obvious,
but in case you didn't know:
Windows cannot run on a G4, except, as previousely stated by eXan:
by "Emulating an entirely different CPU type is VERY hard (thus slow)"
that being said, here is the reason:
Windows is written for x86 processors, it is bascially the language in which
the operating system adresses the processor to do what it needs done.
Windows was not written for, and thus cannot tell your G4 Processor, what
calculations to execute.
Since this is the case, you can regard VirtualPC as being a translator. However the translation process itself takes a whole lot of processing power, thus making it slow. This translation process is called EMULATION.
Now you can better understand what eXan meant:
"Emulating an entirely different CPU type is VERY hard (thus slow)"
Your question was:
"So.....if I upgrade to a MacBook, what would I need to do to run a Windows OS? ..... and would it be as slow as Virtual PC on my Powerbook?"
No, it would run much faster!
To get to the point, MacBooks (the entire new Mac Series) have switched to IntelProcessors (x86-architecture), the exact same processor-architecture Windows was designed to run on. Windows is as responsive as on a PC with similar specs plus the packaging is eyecandy
In case you choose to upgrade, you have two options:
1) Install the Windows of your choice using BootCamp on a separate Partition. In this case a restart is required whenever you switch between OS's
OR
as koobcamuk pointed out
use "Parallels"
2) "it runs natively, so it's like having a windows laptop in a nice case, with osx installed."
which means you can run windows programms directly from OSX. It's a comfortable solution if you use Windows for certain programms needed for work.
I like my Macbook, had WindowsXP running on it till recently, worked fine.
Best wishes,
Toma