Ah, I started out with Slackware too. I don't think you would have too much trouble with any of the various flavors of Linux, but the Nokia guys do mention the Ubuntu distribution by name; so, odds are they've done all their testing with that one.

I currently use Fedora on most of my boxes, but I went ahead and installed Ubuntu on one of them specifically for use with the SDK; I figured it'd be good to get some experience with a Debian-based distribution. (Although I am a long time supporter of open source software, I have never been a real fan of Richard Stallman, and the Debian folks seem way way way too shrill in their support of all things Stallman. At least in Fedora land, you're still allowed to say "Linux" without being forced to prepend "GNU" to it...)