installing it now wouldn't be a great idea as it might overwrite sectors and bytes on your hdd where your data is located.
yes your data is still "there". when you use ERASE or the recycle bin your files are still on your hdd. only thing is windows cannot access it anymore.
windows basically just says "ah this land is open for new construction" but unless you install a new program or copy files onto the "land" on which your data is stored. you have 99% of recovering it.
Go and buy a CD called Symantec View!
You can run the programs like unerase and cleansweep from the cd direct without installing.