According to wikipedia article about Uniscribe http://en.wikipedia.org/wiki/Uniscribe you can get (as this written) the latest usp10.dll from Office 2010 (the last Office to support XP) and slightly updated version 1.626.7600.20796 from its SP1, but you could get it in easier way:
- Download full installer of PowerPoint Viewer and install it ( see comment below )
- or download the smaller PowerPoint Viewer 2010 SP1 then open powerpointviewer2010sp1-kb2460050-x86-fullfile-en-us.exe with 7-zip -> double click ppviewersp1-en-us.msp -> double click PATCH_CAB -> extract USP10.DLL_0002 and rename to usp10.dll. Install the file manually, now that's tricky
- or download the smaller PowerPoint Viewer 2010 SP1 then open powerpointviewer2010sp1-kb2460050-x86-fullfile-en-us.exe with 7-zip -> double click ppviewersp1-en-us.msp -> double click PATCH_CAB -> extract USP10.DLL_0002 and rename to usp10.dll. Install the file manually, now that's tricky