SegoeUI ... where do you get it from to install? And why wasn't it there in the first place? You did not uninstall it?
The font I took it from Vista Transformation Pack for XP (i use Universal Extractor, to extract all files inside), and then i know that Calibri and SegoeUI was fonts created once with Windows Vista. When you install a clear Windows XP, it doesn't came with calibri and segoe fonts. But if you update it, with IE7/8, or you install MS office 2003(only with compatibility pack for 2007), 2007 or 2010, those programs install only calibri font.
I'm pretty sure that i didn't uninstall it, cause there is no such an option. I will put a image to see the difference.