In know that for shure if i had windows already installed i can put Fedora
afterwards but
can i do the opposite??
For example if i format one part of the hard drive in ntfs and then installing windows on that would it conflict anyhow?

If it is XP then it should be the first primary partition, though there are workarounds. Have a look in the tutorials and read about GRUB. Look for Dual boot and info about re-mapping partitions. This is a regular question, and if you do a search you will find lots of answers.

Should be fine.
You will lose grub (and access to Fedora). I believe that Fedora have a rescue option to rebuild grub from the install CD - no big deal.
As mentioned, a million threads on this; and no doubt on the Fedora site as well.

Even if Fedora setup discs don't have the "repair" option mentioned, you can use any Linux LiveCD around to boot up, mount and chroot your Fedora installation and reinstall GRUB from there. It's easier if Fedora offers an "automated" way for this, though.

You can install Windows (any version, really) on the disk, but if you want to get out of that the easiest (though not necessarily the shortest in time) way, consider taking backups of your data (mainly /home I guess), creating completely new partition layout to the disk (Windows partition the first primary partition, rest for Fedora), installing Windows to it's partition first and Fedora over the rest of the disk after that. That way you'll get the partition layout correct for Windows, you'll get GRUB configured the right way automatically and don't have to mess up with moving or resizing partitions and doing odd stuff like that. It's a question of personal taste, and if you're ok with doing some manual configuration, you'll get the installation faster done if you don't reinstall both OS' but just arrange some space for Windows and deal with GRUB reinstallation after Windows is there.