Not trying to be facetious, but you have definitely installed safari 4 and overwritten any earlier versions?
Otherwise, I found this old article, from when safari 4 was still in beta, that suggests it may be related to your graphics card http://news.softpedia.com/news/Safari-4-New-Features-Require-Stuff-105298.shtml
It's the first install, so no worries there. And I'm running DirectX 9. I'm installing a new graphics card over the weekend though, so maybe everything will light up then!
It's not a big thing, but I'm curious to see it! :)
http://support.apple.com/kb/HT3657
Just said I'd post it up here in case any other Win XP user had the same issue. Strange.
Otherwise, I found this old article, from when safari 4 was still in beta, that suggests it may be related to your graphics card http://news.softpedia.com/news/Safari-4-New-Features-Require-Stuff-105298.shtml