My Mini 10 came with XP because, well mainly I wanted the Disk, and I figured if I had to, I would NLite it to scale it down

. I downloaded the Dell Linux ISO which is also free, after trying to install Fedora, Suse, FreeBSD,OpenBSD,Ubuntu netbook Remix well actually a few versions of Ubuntu ...(yes Bittorrent got a workout).
The problem is that don't natively support the wireless card Dell uses. Well they do, but, you will mostly likely have to track down some How-to's, some work arounds, several pots of coffee, .... to get it working.
Not to mention the video responsiveness when changing screens lags in Ubuntu 9.04 desktop including the Netbook Remix aka EasyPeasy which didn't improve even after running updates.
The Dell image is actually a DVD image so you will definitely need a 2G or above USB drive, however so far everything works, but, I haven't stress tested it yet. The Wireless works great with my Linksys Wireless N. I have to say it is much faster than XP. Just my 2 cents.