If you did it, it would be with rebates, and cutting some serious corners. For one thing, i7 ~300, motherboard ~300, ram ~100 for 3 gigs, and the grafics card could be as low as ~150 for a 4850, ~100 for a PSU like the Corsair 750TX. Even then your at ~$950 w/o a case, hd,optical drive, and any extra cooling. I would bump the budget by possibly $200, or look at a P45 board, and a Q9450 or something of the likes.
Here is an article that gives you an idea of the parts needed to compete a full system. TR's Christmas 2008 system guide
That should give you a rough idea and you can look for parts that fit your budget.