are you kidding? the data still there and completelly readable... the only thing is the OS does not read it as files, but simply empty space (mft zone?).
try googling "erase hard drive" and you'll see how you need to get a "kill disk" in order to ERASE it. There is a way for the virus to continue to function (if it was programmed correctly... but it would be very hard).
all of your data will be lost unless you get some hard core hardware to recover it. The department of security (US) recommends overwriting your data 3 times, i think, to make it unrecoverable. This other guy recommends 35 tiems and made an algorythm.
most likely, if not for sure, your virus(es) will be gone by simply reinstalling windows, or removing all the files form your "Temp" folder. If you can boot it up and it is just really slow, then just download ad-aware and put some software on it to remove the virus
The bottom line is, your data will be gone, as well as the virus (which has probably a 99.99999999999999999999999% chance of being deleted)
you should always back up your data before reformatting, because it will be unrecoverable unless it is specially saved somehow (and i dont know how)