a $1000 machine will be far more than half decent. i will gladly give you some build suggestions, but i will need some more information. please fill out all the information as shown here. Please keep in mind that $500-$1000 is a huge budget range, and that i will generally shoot for the upper limit unless you are very specific about your needs: http://www.tomshardware.com/forum/
Since you already have a PSU, dvd drive, hdd, and case, you could upgrade to a very capable machine for around $500. if you would like to step up the overall performance even more, you would probably want to replace the psu and hdd.