You do know that SpecWeb2009 is retired now?
Having said that, the last time I set up for this was a few years ago, and from what I remember, to get it working, you had to follow the recommended steps carefully (verifying as you go along). In particular, you need to setup for an entire Specweb suite test, else it's pointless and you might as well use apache bench or something else.
In terms of documentation/guidelines, I found that looking through reports worked best in showing how the various elements were setup. This is a typical report, scroll down and read the Notes (HTTP Software Notes). That was an IBM originated report, and they discuss a little bit how they configured for apache in this PDF report (see around page-14 forwards).
So, on the whole, I would say:
- ensure you have a good set of guides
- be prepared to configure for the whole suite, or seek another benchmarking solution
- go through various reports and compare their configs with what you have.
- don't be reluctant to start over when things don't seem to be working.
Some documentation links:
- a specweb2009 suggested design document
- of course, the spec2009 user manual (in case you haven't seen it)
- this is a chinese site (i think) but the config directives are in english
- this brief paper talks webserver benchmarking methodologies (seems a useful quick ref)
Hope you find this useful ..