I'm pleased to announce that I've got Dekiwiki running on IIS. Although it does involved a buying (or trialing for 30 days) the FULL version of Helicon's ISAPI Rewrite 2 (3 probably works as well) for the rewriting, the free "lite" version isn't suitable as it doesn't support proxying.
I setup PHP on IIS6 using FastCGI and then installed Helicon's ISAPI Rewrite 2. Then after a bit of working out I ended up with the following rules in the httpd.ini file that contains the URL rewriting rules.
Code:
RewriteRule (/)? /index.php?title= [L]
# in the following rule, $1 contains the whole url
RewriteProxy /@api/(.*) http://localhost:8081/$1
RewriteRule /(redirect|texvc|index|Version|dummy|phpinfo)\.php /$1.php [L]
RewriteRule /(robots\.txt|favicon\.ico) /$1 [L]
RewriteRule /(editor|skins|config)/(.*) /$1/$2 [L]
RewriteRule /error/(40(1|3|4)|500)\.html /error/$1.html [L]
RewriteRule /index\.php(.*) /index.php$1 [L]
RewriteRule /(.*) /index.php?title=$1 [L]
Currently the test server runs Apache/Deki on port 80 and IIS/Deki on port 81, both working perfectly.
According to the mighty Steve...

Originally Posted by
SteveB
#2 can be side-stepped by running dekihost inside IIS. We don't have an install guide for it, but technically, you should be able to run the Dream hosting environment that Deki Wiki uses as IIS HttpHandler (note, you'll need to run from trunk as a bug was recently fixed that prevented from running before).
So when some install notes are put together, we could do this with the free and open source (under some MS license) Ionics Isapi Rewrite Filter.