As far as defrags are concerned, that now occurs silently in the background on a weekly schedule since Vista. As for antivirus software, Kaspersky is probably the most consistently recommended by reviewers, and scrubs up excellently in the tests that the AV-Comparatives labs turn out from time to time (to the extent that it's wise to focus on such metrics). I would also recommend running a quick scan of Malwarebytes (free offline scanner) once a week.

That said, you won't go far wrong with substituting Kaspersky for a free suite like AVG. The highest level of security comes not from one "magic bullet" tool, but from using several scanners (albeit not having them all running at once!) and leaving User Access Control (a much-maligned but rather useful Windows feature) firmly enabled. NoScript for the browser provides a final layer of protection, and then you're all set.

Alternatively, if you're not fussed to the nth degree, just install AVG and forget about it

I hate to play fanboy, but that seems like wayyyy to much work to simply use my laptop!  I like the thinkpads, I be been using them for a decade now at work but if this is what it would take to make it a home machine I think I'll stick with my Apple!

...he said windows does one of the op's tasks for him and recommended a single piece of software to download.

the importance of a good anti-virus has gone down a lot over the past few years, but I just leave a free one going for piece of mind.  i think ms security essentials has the least hassle, but i use avast. avg was always a bit of a pain for me.

Sorry, I must have misinterpreted the part where he said he runs a scan of Malwarebytes weekly.

I do (although I don't bother with NoScript). It takes 30 minutes and doesn't require my presence. I'd say it falls short of "wayyyy" too much work by several orders of magnitude.

save the hassle and order a Lenovo ThinkPad preloaded with Ubuntu linux!  (Linux Mint 14 is also a good choice, with the cinna-mint flavor being my current favorite)

no AV needed, as it follows the same permissions scheme as OSX [both crafted from UNIX], and faster than windows to boot! (pun intended)

I've run both and Ubuntu has a slight lead. Mint with Xfce is even faster, though...
(on an ssd, mind you.)