If Win7 wasn't originally installed, then there may not be a recovery partition. You will need to remove the HD in case it causes all sorts of issues and deal with directly in order to reformat it, etc.. i mention that in case you have a bad HD.
Otherwise, using the Win7 DVD, do an install. Again, if not originally installed, you will need any or all drivers required, so before formatting or deleting anything, retrieve the required drivers, etc.. Win7 install may accept older drivers if actually needs them on a 1-for-1 basis if at all. Formatting will remove the old OS and if factory re-install that should all that needs to be required, that DVD disc.