Hi i've always tried to install multiple linuces on my desktop but in vain. I want to dual boot FC 6 with Ubuntu. How many Linuces can i have on my PC. Are there any restrictions????

How do in go about installing them????

Linux doesn't "do" restrictions... you can install many many many, not even sure if there is a theoretical maximum depending on what you would define to be a different version. i've seen projects literally booting over a hundred just for the sake of it. either way, install each distro into a seperate space on the disk, and the 2nd one will more than likley recognise the presences of the other and add it to the boot menu. fedora 7 is out now btw...

I have like 8 different distros installed on my HD's with no problems. Since you're using ubuntu, I guess you installed with the live cd?? if this is the case then you probably have ubuntu's grub installed on the MBR. All you have to do is to install FC, without installing grub in the MBR, then boot Ubuntu, mount your FC / or /boot partition (depending on your setup), look for the /boot/grub/menu.lst file, copy the entry for FC, then open Ubuntu's /boot/grub/menu.lst and paste the entry for FC you just copied from your FC partition, save the file, reboot and you're done.

If you installed FC before installing Ubuntu, then you'll have to follow a similar procedure (anyway, if you're using Ubuntu's live cd it should detect FC during installation and add the respective entry for it on grub's menu.lst; otherwise, I'd suggest Ubuntu's alternate install cd which allow you to specify the grub installation destination).

I too have many Linuces installed--actually, I have lost track.....

Some booting tips at my site (link below). I included a link to some Saikee posts (he is the multi-boot super-guru)