What are the methods for getting an old, used windows P.C. ready for secure Bitcoin usage? Let's say I am about to set my Grandmother up with a wallet. I have no idea what she has on her computer. There could be a host of malware, keyloggers etc. Let's also say that a complete wipe and reinstall is not an option. 

I was thinking of what steps I could use to give the maximum protection.


I could use CCleaner to wipe any temporary files. This will remove any excess past data she has generated.
I could then use a program spybot search and destroy to check for any malware. 


What else could I do to check if there are any threats on the computer?
If a reinstall is not an option for you then you should do the following:

Requires: CCleaner


Boot in Safe Mode so that any malware start up entries don't get executed.
Use CCleaner to clean up disk space and registry.
Inspect the Start Up list for any suspicious/unwanted entries and
remove them.
Reboot the computer.
Use any anti-virus to remove any present malware and clean infected
files.


This should clean your old pc.

Source: Experience