on your g4, it'll be roughly (very roughly) like running windows XP on, say, a 266mhz intel 386.
i realise that 386's didn't go much faster than about 40mhz, but that's the crux of the analogy, the emulated 'clock speed' is roughly that of a 10 year old processor, but the optimizations are that of something nearer 15 years old.
it's slow. not impossible to use, just, don't expect miracles. IE will work fine, as will word, solitare, lightweight windows applications. it's a testing ground, not a platform in its own right. test a webpage you've designed for example, but i wouldn't try and play games. nothing newer than a DOS game is about the level you're looking at in terms of power.
also, it has very little support for peripherals, including graphics and sound hardware.