When it comes to the over the counter computers, I had good experiences with Gateways ($$), and GREAT experiences with Sony Vaios ($$$).
If I were to get something new on  a budget I'd scour Ebay for a year or so old Vaio. You can find really really decent computers for around a $1000.  Considering your computer seems to be about 5-6 years old, you could get a screamer (in comparison) for that much money.
Perhaps spmething similar to this: http://cgi.ebay.com/Sony-Vaio-VGC-RA830G-P4-3-4-Ghz-1GB-320-GB-Media-PC_W0QQitemZ200066114779QQihZ010QQcategoryZ140074QQrdZ1QQcmdZViewItem

If you want to go with the latest and greatest, Personally, I'd have it custom built by a place like this outrfit: http://www.xicomputer.com/products/mtowersp4home.asp  (They happen to be local here to me) and I've known the guys for years. They build awsome computers.

Or I might go for an 'over the counter' computer... 
Personally I tend to stay away from HP's Dells, and Especially E-machines, since I had bad experiences with them.
For the last year I've been using a high end Gateway at the office, for 3D terrain modelling, and I'm pretty darn happy with it. So, if I were to run to Best Buy or Fry's and get a new computer, Gateways are probably the first one's I'd check out.

Considering that I don't go with the latest and the greatest, and at the moment I'm not in a splurge mode, I'd [probably pick up a Vaio from Ebay. I have 3 Vaio's at home, one is probably 6 years old or more, and it's still ticikng like a  swiss watch (at it's mighty 1.2 GHz) (LOL)

The Dual Core E-machine I got myself talked into about a year ago has taken a big dump since I got it, and it's turned into a bookend.

Hi, my namez: "NO, Bad Kitteh, NO!"  Whaz yurs?
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