To learn about Uniscribe, please see Chris Fynn and David Germano's article Instructions for using OpenType fonts for Tibetan in the MS Windows Operating System. To install USP10.DLL on your system see their article Updating Uniscribe to a Version with Tibetan support, especially Instructions for Individual Applications. You might also want to see Upgrading Uniscribe (USP10.DLL) on Windows 2000 System - it mentions that you can join Microsoft VOLT User Community and obtain a recent version of USP10.DLL for free.
Internet Explorer displays Tibetan Unicode correctly on Win/2000 SP4 and Win/XP SP2 if USP10.DLL is copied into the application folder.
Unfortunately this sets all Unicode to use the Tibetan font. Most Tibetan Unicode fonts have only limited support for glyphs outside of Tibetan and ANSI. Tibetan Machine Uni is the best choice. These browsers displays Tibetan Unicode correctly on Win/XP SP2 if USP10.DLL is copied into the application folder.
Opera displays Tibetan Unicode correctly on Win/XP SP2 if USP10.DLL is copied into the application folder.