the MSI is a good card. the main difference between the ti200 and ti500 is SPEED. the core amd memory speed are supposed to be faster. i.e., faster ram and faster core. But a lot of people are just buying the ti200s and overclocking them to ti500s. i woudl think you could overclock the ti500s more, but i would recommend sticking with the ti200, as a ti200 @ti500 speeds is plenty fast, and only half the price
you know, turkey does make a good point. i am not gonna say you should go out and buy 2 cards, but you may want to wait a few more weeks until the rest of the gefroce4 line is released. by that time, the prices on the gf3 shoudl drop a little. i think that you can already find the MSI card for $150 + around $15 for shipping. if you want the card soon, and want a good geforce3 but arne't SET on buying the MSI, you may want to head over to teh HOT deals forum.
in the hot deals forum, they have deal on the gf4 mx series card (lower than gf3) for aroudn $120, and deals on the visiontek GF3 ti200 for $150 with a potential of getting it at $100 if you have an amex blue.
in my eyes, i'd jump on this visiontek cuz $100 for a GF3 ti200 cheap. and you can o/c to to ti500 speed. plus you save money

good luck