If installer does not work for you here is a manual process until we solve the errors.
1. Download
http://warden.eurobattle.net/downloads/file/4
2. Extract into Program Files
3. Move w3l.exe and w3lh.dll into W3 folder
4. Run euro.reg
5. if your W3 folder is different than C:\Program Files (x86)\Warcraft III go to Regedit->HKEY_CURRENT_USER->Software->Eurobattle.net and change w3dir key to your proper directory.
6. Also make sure that Regedit->HKEY_CURRENT_USER->Software->Blizzard Entertainment->Warcraft III->INSTALLPATH is the same as w3dir
7. Try running client as admin
You should now be able to do everything as with normal install.
Please report your installer error anyway so we can try to solve it.