Ages ago, back when httpsrvr first came out, I got it working with Apache for a client. Recently, I came across a post by Sydney Delieu in the borland.public.datasnap group outlining the steps needed to get this working today. It strikes me that things are quite a bit easier today than before to get this working, but I did test these directions, and they work well.
I use Apache 2.0.52 with httpsrvr.dll. To get it working:
1. Install Apache (I will assume default directory structure for 2.0.52).
2. Copy 'httpsrvr.dll' to your /apache2/cgi-bin directory.
3. In httpd.conf, change the 'Options None' (again assuming defaults for 2.0.52) in <Directory "C:\Program Files/Apache Group/Apache2/cgi-bin"> to 'Options ExecCGI'.
4. AddHandler isapi-isa .dll to your httpd.conf.
5. Restart Apache.