The PS2 linux kit isn't as open as you might think, however...
I have a ps2 with the linux kit on my desk at work, and while it's quite good value, and a lot of fun, there are limitations. Sony tried quite hard to make it tricky to get raw device access. We can't have users extracting CDDA from CDs, can we? Oooh no, they might use the ps2 as a network jukebox, dear me no! (etc).
Also, it doesn't use a standard linux kernel tree, so forget snarfing down the latest and greatest from kernel.org to get those VM fixes. It uses a special Sony tree, where "special" denotes "surreally old and outdated".
The distro that sony supply is effectively an old Redhat variant, too. This isn't to many folks' taste (certainly not mine), and it'd be distinctly non-trivial to port something else to it (slackware, debian etc). This is obviously less than ideal, too.
You need access to a VGA monitor which supports sync on green for the initial install, too. However, after that, you can use a TV or whatever you prefer- strangely reminiscent of the halcyon days of blurry ZX Spectrums.
There are some endearing things about it. The first being that for your 200 Earth "quid", you get:
o Special hacked crippleware 40 gig hard drive and interface gubbins*
o Ethernet adaptor
o Sleek PS2 branded USB keyboard (though I prefer using a Sun type 6
USB keyboard at home, it suits my ungainly shovel-like hands a little
better

o Cute little PS2 branded USB wheelmouse
o An install DVD with the entire distro - no more install time disk swapping
o A VGA adaptor - needed at install time, but also nice for games which
manage progressive output (these are rare- tekken 4 anyone?)
The other thing that I liked was the way that the kernel that you're using bootstraps from the memory card, which is *very* cute indeed (though you'll need to set aside a memory card entirely for linux).
There are some nice projects which allow access to the vector processors, GS and other bits and bobs from within linux, and a decent amount of documentation, and a "scene" with nice free third part demos, little games etc.
So nice try Sony, I was very charmed by the effort, even though it's less than perfect. However, check that what you want to do isn't verboten before making any elaborate plans for world domination with your ps2.
More info is available at
http://playstation2-linux.com - some of it a lot more accurate and up to date than the above too, I'll wager; I don't really have enough time to play with the ps2 at work these days...