Installation Files, Service Packs and Hotfixes?

Hello there,

I've just started a new role which requires me to go into companies and
install third party software on Microsoft Windows Servers (2000, 2003, etc.)
so that various new systems can be implemented for that company.

Some of the software I install has prerequisites of the Windows Server, for
example that IIS, IAS, Microsoft Message Queue, .NET framework, DHCP Server
or whatever is installed for the third party software to function correctly.

Sometimes these prerequisite services are installed but more often one or
more will need installing on the Windows Server.

I was wondering what the correct course of action should be if the Windows
Servers asks to be pointed to the Windows installation files (I can't
remember the exact message - maybe something to do with an i386 folder or
the installation CD or files).

What I'm getting at is this - if the server is a base build and has had no
service packs on then pointing to the original installation CD would be
fine, but what if the server has had one or more service packs on it? If
you give it the original installation CD when it asks then won't it be
putting on old software and drivers which may cause a problem?

If installation files are asked for then does the i386 folder on the machine
contain the files from the latest service pack and so it would be fine to
point to this? Or should I first find out the spec and SP level of the
server and obtain a copy of the relevant service pack that the server is
running and carry it with me, then point to these files if asked for
installation files?

And then what about hot fixes and security updates? If the server has had
updates since the last service pack (quite likely) then even pointing to the
files in the service pack that the server is running might get out of date
files and drivers might it?

Is there a best practice for installing extra MS Server services and
applications with regards to where to get the files from when it asks?

Any advice appreciated,
Thanks,
Pete.

P.s. Please reply to the group as I've not put my correct e-mail address in
this accout for fear of more spam.