I came up with the idea that it would be good to get Nessus to import nmap port scan results, parse the results, then perform the service/port specific tests. The main reason being the duplicated port scans and unless you configure Nessus in a specific way then you might not get good/full port scans. The duplication means spending more time waiting for scans and I am sure that most people would prefer getting root or going to the pub, rather than watching port scans?

Anyway google told me about "nmap.nasl", which is a plugin that allows you to run port scans using nmap from Nessus. It can also allow you to import nmap port scans, great eh? Yeah if you run *nix, since no plugins work in Nessus that require external tools, great. So I have written my own "nmap.nasl" equivalent plugin e.g. nmap_grep_importer.nasl

To use the plugin, you have to copy the plugin to your Nessus plugins directory e.g. C:\Program Files (x86)\Tenable\Nessus\plugins. Then get a command prompt up and run the "build.exe" application, it creates a new plugin cache database, like so:

PS C:\Program Files (x86)\Tenable\Nessus> .\build.exe
Rebuilding plugin database...
Installed 23144 plugins
Done!

You might have to add/modify a registry string value to allow the use of unsigned plugins, although it didn't e.g.

Vista:
[HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Tenable\Nessus]"nasl_no_signature_check"="no"

XP:
[HKEY_LOCAL_MACHINE\SOFTWARE\Tenable\Nessus]"nasl_no_signature_check"="no"

Each time you run "build.exe", it's probably best to delete the following files, since it appears to cause some very strange GUI issues in Nessus Client:

C:\Program Files (x86)\Tenable\Nessus\plugins\plugins-code.db
C:\Program Files (x86)\Tenable\Nessus\plugins\plugins-desc.db

That action will import the new plugins and allows the Nessus Client application to display the new plugins. The plugin appears in the "Port Scanners" section of the Nessus Client. So create a new profile, select the "NMAP grepable Result Importer" port scanner, go to the "Advanced" tab of the Nessus Client, then select the "NMAP grepable Result Importer" option. Select your NMAP grepable result file. Hit scan.

Download it here.