This seems incredibly slow to me, especially for raid 0
Raid 0 will actually have worse seek times if anything
I'm more of a Linux guy than Windows so I'm not much help here, I don't know much about Vista other than it's buggy and slower than XP, it sounds like the drivers are to blame but I could be completely wrong. Also check to see if the drivers are in "silent" mode, that will make the seek times much worse.
the slower access times are to be expected for software based onboard raid 0 (best case scenario for raid 0 is that youll get within 1ms slower than a single hdd would)... vista IS slower than xp, it tends to use up more cpu cycles, even when idle, which would result in poorer raid performance in general anyhow... you could have also had additional activities and unnecessary processes running during the testing too, which would give worse performance than if absolutely nothing else was going on
all in all though, i would say your results are within normal range (some 7200s are about that slow for random access times anyhow, and having those particular hdds in raid 0, certainly wont do anything to improve their times)
edit: the only way youre going to get noticably improved access times, is by using a hdd with higher rpms (10k and 15k), or by going with a solid state disk, which has sub 1ms access times, i believe... other than that though, again, your current access times appear fairly normal