How to secure my computer?

[Wolfy]

So, alright, I have my computer, and someone else's computer in the house, on the same network.

Now, getting my own network is out of the question, pretty much, so how do I go about making sure mine can't contract a virus from theirs, since it seems that it might be infected?

[Autumn Sativus]

So long as you're not sharing files with that computer, you should be fine. Just make sure you go into your file sharing settings and turn them off. Protect your computer with an anti-virus (I recommend Microsoft Security Essentials, which is free) and run a Malware Scan (try Malware Bytes) once in a while.

[Wolfy]

Will Malware Bytes and Security essentials co-exist peacefully? ;/

And..I do believe I have all file sharing turned off.

[Autumn Sativus]

Yes, they are two different types of programs. While you don't want to have two anti-virus programs running at once, Malware Bytes is not an anti-virus program.