Try booting with maxmem=3072 or maxmem=2048, if the problem is indeed the broken AppleNForceATA that should stop it (by limiting your available memory).
If you still get panics when downloading large files with that then its something else.

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AsRock P45TS | C2D E8200 | GeForce 8600GTS
Mac OS X Snow Leopard 10.6.1 + Windows 7 Ultimate 6.1.7600 + Fedora 11