A couple months ago I installed XP onto a ThinkPad X120e; being the first dual-core AMD ThinkPad the hardware is relatively emaciated, and I wanted something lightweight and productive for it.
I used legacyupdate.net to apply all available important and recommended updates, as well as some nice-to-haves such as updates to the .NET infrastructure. I have been using the Supermium browser, which is an up to date fork of Chromium for older versions of Windows, including XP. All of this has gone off without a hitch, and the laptop has been great to me with its current configuration.
Recently in the tech news sphere I have seen articles exclaiming what a bad idea this is, demonstrating how connecting XP to the internet for just a few minutes leaves it riddled with viruses. Decided to run an MBAM scan with updated databases to see for myself, and it's totally clean.
In other news, this thing is a great little Diablo II machine. I'm maining necro right now.