What validation/qualification should be done on instruments with built in microprocessors? What should be done for IQ and OQ of these units?

Qualification/validation requirements for non-configurable standard software packages
Software packages (Non-configurable standard software packages - types of validation needed (qualification or validation)

To what extent should network be qualified or validated? This includes both the hardware and software?

In computer system the term validation is used for what is understood as qualification for equipment that support a manufacturing process because the data collection and work out is then defined as "Process".

For built-in microprocessor there is still a big discussion whether this should fall into the scope of 21 CFR Part 11.
What we do in practice for microprocessors is the following: in the IQ we record the serial number if known, type of microprocessor and where applicable the software version that is downloaded on it.
For the OQ we verify that the functions driven by the microprocessor are properly controlled e.g. in the case of an HPLC pump that the flow rate is accurately controlled according to the vendor' s specifications.

Concerning standard software packages that are not configurable (does it really exist?) the IQ/OQ extend is well defined in the GAMP guideline for example.
Our approach in the IQ is to register the name of application, the license/ serial number and to document the successful installation of the software based on vendors instructions. A good test whenever possible is to compare the installed files with the list that the vendor gives. We also verify that we get the users' instruction/manuals shipped or have a CD for that.
In the OQ we would verify the critical functions of the software which will be most often used in the future. You can also perform stress tests for the system i.e. send or receive large amount of data. We also get assurance that we get trained by the vendor if this is possible...
For the validation or PQ the software is run its usual environment.
But do not forget once: the software is not all, you have to qualify the harware as well, so the network for example. Network IQ would include network schema, with identification of all components and measurements of cable performance. Network OQ could include data exchange tests and all configuration set-up that are installed.

Anyway the answer to the question depends much on the criticality of your systems. I would recommand you to have a look at the GAMP guideline or try the web site of "labcompliance" or "IVT", you can find helpful hints on many web sites.