You will need the 25-digit product key on the bottom of the notebook in order to reinstall Windows. Jellybean Magical Keyfinder is a way better tool for finding the product key of the OS without navigating through the registry, as well as allows you to save it to a text file.
Do this is if you HAVE an OEM partition: Boot into the BIOS and there may be an option (most Acer notebooks have D2D recovery etc.) and try to do a recovery from the partition. In some cases I have seen where you do in fact need a Windows install DVD in order to complete the recovery.
Do this is you have no OEM partition: Find yourself a local computer shop and ask them if they can burn you an OEM Windows 7 disc. Show them that you have a product key for it and that you just need the disc. Offer money if needed to cover the cost of the burning of the disc and the cost of the DVD. The only valuable thing about owning a copy of Windows is that 25-digit product key, not the disc as it is the license to use Windows. Once you have the disc in your possession , pop it into the notebook, boot off of it and delete all partitions on the HDD, then create a new partition and install Windows on that. Of course, BACKUP IMPORTANT DATA FIRST.