If u have enough space then u can complete this task. do one thing u just make 3 partition in current O/s then whatever data u have I 2ND partition take full backup of that and save it in other partition, then turn off your laptop and also put O/s DVD or CD in the DVD drive, and from boot make It first boot able device and Install This O/S on that partition which is fully blanked, after u Installed the O/S, while U will be Opening your system It will show U both The option weather U want log in on win XP OR win 7. I hope It will be helpful for u.