I've tried a Wordpress installation myself and it worked fine. What I used is this:
ToolkitID = wordpress
RequestURI exists Exit
Match .* Rewrite /index.php
Hostname = www.domain.com
WebsiteRoot = /path/to/wordpress
StartFile = index.php
TriggerOnCGIstatus = false
UseToolkit = wordpress
The Toolkit settings are only necessary if you plan to use permalinks. The error during installation is probably caused by the CGI Status error which is generated by Wordpress. The TriggerOnCGIstatus setting handles that problem.
Please let me know if this solves your problem.