Just FYI - but according to initial reports, the GF4 MX420 is gonna be the runt of the bunch. The better card is going to be the MX460 which, according to "leaked" specs, which you never really can trust much, will be about on-par with the Ti500 when it comes to core/clock speeds. For reference purposes, take the retail prices between a GF2 MX200 and MX400 and you'll probably get the price difference (give or take 10-20 bucks) between the MX420 and 460.
Caveat Emptor, too - I remember when the GF3 came out that everyone was saying how it was going to revolutionize gaming and soon every game was going to use its unique features. Well, Aquanox still isn't out, the Giants remake with "GF3 Enhancements" did basically nothing and fewer than 10 games give you any real "boost" in visual quality using the GF3.
Don't get me wrong, I love nVidia products, but don't get so caught up in the hype that you get run over by the bandwagon.