Is AVG with Windows Defender adequate PC protection? Or, should I renew the improved Trend Micro PC-cillin?

its good enough just update

Yes, adequate but little more. If you're going for freebies then AntiVir and Avast are both better than AVG (use either, not both). Windows Defender is useful for the real-time protection but it isn't the greatest. Use it with Malwarebytes' Anti-Malware and/or SuperAntiSpyware (both free, no real-time protection). Use these whichever AV you go for.

If you're going to buy an AV, there's better than Trend, i.e. NOD32 / Kaspersky.

You also need a good, two-way, firewall, i.e. OnlineArmor or Comodo (both free).

Use Firefox with NoScript to protect you against malicious scripts hidden on websites and use Secunia PSI to keep *all* your software up-to-date with the latest security patches.

http://www.avast.com/eng/avast-compare-home-profes...

http://www.malwarebytes.org/mbam.php

http://www.superantispyware.com/

http://www.tallemu.com/free-firewall-protection-so...

http://www.mozilla.com/en-US/

https://addons.mozilla.org/en-US/firefox/addon/722

http://secunia.com/vulnerability_scanning/personal...