You can recover some files if you made a fast format of your partition while installing windows. Fast formating will only delete the table which stores informations about where the file is physically on the disk.
Some recovery tools will scan you drive, and if it find some files it will recover them.
But you won't recover everything. You have certainly crashed some data at the exact location where the new windows installed.
You can try to find some data recovery tool. Here is one which provides one gig of data recovery for free : http://www.easeus.com/datarecoverywizard/free-data-recovery-software.htm