The PS2 port is better then the Dreamcast port. Superior controls due to twin analog sticks, faster frame rate, sharper and more detailed graphics, faster loading times, and more efficient saving. Also has the cooperative game of Decay, the only part of the Half-Life saga that PC owners never recieved (Although there's a homebrew remake of it available for PC). It isn't just a cooperative mode for Half-Life, it's a unique expansion pack with it's own storyline telling the story of two scientist, much like Blue Shift and Opposing Forces were.
The only reason to burn Half-Life to cd-r to play on your Dreamcast is because it's free and neat to check it out. And it has the only console version of Blue Shift, a nice expansion pack that Half-Life recieved (Which was actually created first for the Dreamcast and only later ported to the PC).
In all honestly though, if you want the superior experience and really want to play through the Half-Life saga, spend the $10 or so that Half-Life 1, Blue Shift, and Opposing Forces (Which isn't available on consoles) costs on Steam and play through it there. It's an amazing game and my favorite first person shooter, and both expansions are also excellent and worth playing through before moving on to Half-Life 2 and it's various episodes.
And any PC that virtually anyone is using for day to day use in 2010 can pretty much easily run it maxed out. And if you're a Mac user, I hear the entire Half-Life series will be coming to Mac users pretty soon as well.