I have windows XP and FC4 installed but i later removed Linux
now i would like 2 install FC4 using 20gb & Mandrive using another 20gb
how would i go about installing the 2 Linux along with Windows Xp on my single hard drive?

Install Windows first. Then, you can choose to install either Fedora or Mandriva after Linux. Just make sure to install in different partitions to do not overwrite anything. The last OS you install (Fedora or Mandriva) should be able to automatically configure GRUB or LILO automatically to recognize all the 3 installed OS'es. It's nothing difficult, really.

First of all install windows. Use FAT32, NTFS is not fully supported yet and you need to download additional RPMS to mount NTFS under FC.
Then, Mandriva. During installation of mandriva, install GRUB or LILO in the root partition. Then install Fedora. Install GRUB (LILO is not available with FC. It is available with RHEL though.) in the MBR.
This way all the three OSes will be recognized.

There is another alternative. I use Acronis OS selector. It does the job very efficiently. It costs a lot but it is highly efficient as has many utilities like partition resizing, converting file system types. I have 6 OSes on my system right now namely Xp, FreeBSD, Mandrake 10.1, Ubuntu 5.1, FC4 and PCLinuxOS.
Hope this helps.