depends on how long it'll take you to afford the GF3 (but if it's less than a year)
get the Radeon LE
if you OC it and then tweak the Hyper-Z you're golden
if you do that it'll beat the MX (I dunno about the MX400 or the GTS, etc. - but I expect it should be able to hold it's own with them)
The Radeon Le is only around $70
This will save you money - and that money will help you get the GF3 sooner
But if you only want to get GeForces, then, get anything but the MX 200
here are the tests that show the LE doing great (look at it's stats when it is OCed and has the Hyper-Z - that'll give you a good idea as to how good it is...)
edit -
You asked "Which GF2 MX should I get?" and even though this isn't a GF2, I think you'd be better off with it... that's just my opinion though