If Install Arch on my machine is there any danger it will overwrite Suse or Win XP ??

There's always that chance whenever you install a new OS. Just be sure you are installing to free space on the hard-drive, or known unused partitions.

You also need to be careful with which OS will boot the system.

At the moment I have no unused partitions.
How can I create one ?

You need to resize one of the existiing partitions. This is where the risk comes, as there is always a chance that the resize will kill the OS on that partition. On the up side, arch can use the same swap that you use for the other linux OS.

I have a disk set up with 4 partitions. ..

xp 6gb
arch 6gb
mdk 7gb
swap .5gb
/home 20.5gb

The home partition is shared between the arch and the mandrake distro (works nicely, esp if you use the exact same desktop on both OS. I started with a 12 GB xp partition and resixed it to install the arch one. This killed the XP install and I had to reinstall. I have seen threads where the resize was successful though.

There is a free software solution to resize partitions: GNU parted. There's even a graphical, partition magic like, frontend: QTParted. You can get RPMs there that apparently work with Mandrake, too.
Hope this helps, best of luck!
-bbp

How did you do the reinstall ?