I only use the computer for mixdowns myself so I'm not as knowledgable about these computer multitrack programs and soundcards as some of these guys are, but there are a couple of things I'd like you to consider in your purchase. One important thing is, will you be recording instruments (via microphone) in the same room as the computer? It takes a good pentium 3 in my opinion to get the porformance you need for doing multitracking on a computer, and the problem with the better, (i.e. faster) pentium chips is that they need a good cooling source, so most computers that have a Pent3 in them have a large and noisy fan that will certainly be picked up by a microphone. Mine is so loud that I can hear it down the hall in other rooms!
Something else to consider is maybe taking a look at the new Boss digital 8 track. It's only about $800, and is a real bargain. It doesn't have any XLR inputs or phantom power though, so if you plan on using decent mics in the furture, you'll have to buy a couple of good mic pre-amps. It also only has a couple of inputs, so you can only record 4 tracks (I think) at a time. While it has a mixer with a lot of useful features including cmos (for guitar amp and effects simulation) and some really terrific effects, you're limited to having to input all your channel mixdown changes, one channel at a time since the units mixer is "internal" and there isn't much by way of external controls--i.e. knobs. This is the way it is with most of the value priced digital recording mediums though and unless you spend a lot of money on a fancy soundcard with a lot of ins and outs on it, along with a good mixer, you're still going to have that same problem when recording on a computer. There's a lot to consider....