well, here's the basics of what you'd need to do. Add the new domain into the panel, then using SSH copy all of your files from site1.com to site2.com. (see wiki article on SSH). To do this you'd use the command:
cp -rf site1.com/* site2.com
Next you'll need another database, set that up through the panel. Then dump the data out of site1's database and fill it into site2's database. See wiki article on 'migrate mysql' for help on that one.
Then you'll have to edit configuration files for your stuff at site2.com to point to the new database. With luck, and perhaps a little tweaking you should have two running copies of your domains.
Let me know if you need further explination.
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