1. How paranoid are you ? If you have your laptop drive partitioned so only the OS is on C:, then erasing all of your D: drive is probably good enough. If you have been operating with everything on C: then it gets more complicated. Unless the laptop came with OS disks which you can locate, or a hidden partition to allow a restore to 'original factory state', keep in mind, depending upon the level of sophistication of the charity, giving them a laptop which has had the OS completely removed may be of little use to them. If they say that's OK, then the util available here:
http://www.pcworld.com/article/2084977/hdderase-exe-review-freeware-utility-securely-erases-drives-the-old-fashioned-way.html
will deliver a drive that's clean, unless your charity actually works for the NSA.
If you have just the single logical C: drive, and no ability to restore the OS and they need it... then I'd uninstall any programs, disable rollback and then erase all directories except Windows.
2. No single anti-virus works perfectly, the best practice is to use a multilayer approach which means finding apps that play nicely together. I've been using the following 3 all live at the same time, they do NOT interfere, are available cheaply and don't even together use 2% of my cpu power:
A. The MS Security Essentials (that's what Win 7 calls it, it's Defender in 8 I believe is free and almost worth it...) seriously it's the weakest but can't hurt to run and inoffensive
B. Been using Webroot for years, their SecureAnywhere which is now cloud based seems very good, includes lots of useful extras (a Password manager, an easy to use Sandbox, coverage for my Android cellphone (Moto Electrify M) and, ahem, one subscription seems to work just fine on several boxes...
C. Eset NOD32, just their AV product, NOT the full Suite, has always been known for it's small size and lightweight use of resources, it's also 'insensitive' to being installed on multiple boxes with a single sub so instead of buying a sub for multiple machines, google looking for a sale on a multiyear sub.
I go to many many 'unsafe' locations, Webroot and NOD32 alternate on which stops me sooner and nothing even slightly serious has made it onto any of my boxes. Keep in mind all good programs do need to be configured, just buying and installing without ever even looking at the setup options will NOT produce anything near optimum results, especially since most programs today also 'stop/warn' for 'unwanted apps' (like browser toolbars) and cough cough 'legitimate cracks' which some of us sometimes actually want to investigate...
