Here's a couple of Vista file system tweaks I've been using. The one referring to LargeSystemCache didn't seem to have any effect on my XP machine with 1 GB ram. But on my 2 GB Vista PC I noticed that HDTune Minimum benchmark, which always troughed into the single digits, now stays up over 30 MB/sec. In any case neither tweak seems to have any negative effects that I can detect.
fsutil tweak
LargeSystemCache tweak
fsutil tweak
LargeSystemCache tweak