How can i write zeros to a file/disk very fast?

i need it to make a "Low level type format"

Writing zeros is not a low level format. Low level formatting involves placing the sectors and tracks, and is only done on floppy disks.

I disagree. You can do a low level format on a hard drive. Usually hard drives come with a cd-rom or an iso can be downloaded with a utility that will do a low level format.

As far as doing a secure wipe you should look into DBAN. I think there is information on their website that will tell you how to do a secure wipe and it can do a secure wipe from a bootable cd-rom itself.

Filter: those tools also just write zeroes - as a end-user, you haven't been able to do a true low-level format for years.

If you want to extend the file size filling it with zeroes then I think that SetEndOfFile should be the answer http://msdn.microsoft.com/library/default.asp?url=/library/en-us/fileio/fs/setfilevaliddata.asp

SetEndOfFile is nice if you just want to extend a file - it's almost a zero-overhead operation on NTFS, and makes sure the file is as little fragmented as possible. Takes a while on FAT filesystems though.