Are you asking how to quantify someone's LAMP experience or are you asking how to interview someone for a programming position? Seems like the latter to me.
Or you could just release unfinished games like STALKER and STALKER 2 and just never fix them.
Don't get enough buyers or have some financial trouble? No problem, just screw all the customers who purchased the special edition pre-Alpha version and who you've tricked into doing free QA for you.
Here are some better ideas.. Release good completed games and continue doing so. Stop trying to nickel and dime your customers.
The support cycle for Windows XP SP2 ends on 2010, so it probably isn't the best investment to buy it now... unfortunately. MS may extend it past 2010, but who knows.
Vista Home runs $99, though IMO the interface is a bit too confusing for older folks, especially with the constant nag of "Are you sure you want to do xyz?!?"
Linux is free of course, Ubuntu is decent and easy to install, you may consider Ubuntu 8.04 LTS (Long Term Support). The support cycle ends in 2011, which is considerably longer than many (most?) other distributions.
Maybe just get them an iMac, the current refurbs will cost you about $1000 or get one of Craigslist/eBay/etc. Just set it up and leave it alone. In general Apple hardware resells a higher value than any comparable PC hardware, so if you eventually need to upgrade them you can get a bit of money back from your initial investment. Setup TimeMachine to automatically backup and you're good to go. As with linux, you can install OpenOffice and many other open source tools.