I assume you've been to http://www.avid.com/cgi/forumscgi/fo...=45&LastLogin=
and have read what the users of Express Pro have to say - some aren't too complimentary, but then again, you don't hear as often from users who aren't having any problems.
As to whether to go with a Mac or a PC, I'm sure you'll find as many biased people here on sagerforums as you will on the mac forums, so we're probably not much help in that regard. As to which PC editing system to use, I'd agree with Steve, that Adobe Premier Pro is probably the biggest bang for the buck, especially if you plan on doing work mainly on your own projects.
However, if your aim is to eventually make your living as a freelance video editor or in the broadcast industry, then I'd have to say Avid is the way to go. Even with the in-roads FCP has made, and even if FCP is better than Avid Express Pro (that's debateable), Avid is still the de facto broadcast industry leader. And that's mainly because of its sophisticated higher-end products aimed at broadcasters and the film industry, as well as the huge number of Avid systems now in use when compared to other NLEs. As has been stated, the learning curve on the Avid is steeper than the rest because it is a more complex system, but once you've learned on the Express Pro you've at least got the fundamentals of learning on even more sophisticated Avid systems and, hopefully, some interesting work in the industry.