Put Linux on it, and do not run any browser plugins or extensions, and do not use Chrome for Linux (it is closed source) on it.
Such a PC should only be used for your bitcoin activity, not general browsing. Not even browsing this forum. Just use it for bitcoin.
You can run a wallet on your normal PC just like you can keep some fiat cash in your leather wallet, but keep the value low.
btw flash (even in Chrome) is dangerous because flash allows programs loaded from web pages to manipulate the clipboard. Get rid of flash even on computers that you don't use with bitcoin.
Good information here. I have been trying to do all bitcoin activity on only ONE computer in the house, with no internet browsing.