I've just been assigned a task of working (learning) WIX. To better understand the dialog handling and stuff, I found many references of "just get..." and then WixUI_InstallDir.wxs and InstallDirDlg.wxs (and obviously the others out there).
I've searched all over (several hours) and have YET to actually find the raw .WXS files these other links have directed me to.
Thanks for the help...
For version 3.5, the source code is at http://wix.codeplex.com/SourceControl/list/changesets?branch=wix35