Depends on what you mean by "wiping out my harddrive". Eraser can only erase the files and freespace, so it will not affect the formatting of the drive.
DBAN is a different product and is used to overwrite the entire drive, or specific partitions. If a partition is overwritten with DBAN, I believe it has to be reformatted before it can be used. If the whole drive is erased, it has to be partitioned and formatted prior to use.
so after eraser erases the files then I can go ahead and reformat the harddrive because I want the drive to be blank. So even if I don't reformat, I don't have to worry about people trying to recover data from the drive after eraser deletes all the files. thanks.
...as long as you not only erase the visible files, but also do a freespace wipe. However, since you want the whole drive wiped, you may want to use DBAN instead. If you are trying to erase the drive that Eraser is located on, that won't work very well, will it. It can't erase itself or Windows and continue to work.
DBAN boots up from a CD and bypasses the harddrive, so it can remove all information from the harddrive completely. From your description, I'd go with this approach rather than Eraser.