Im using ubuntu desktop edition for my server (for some test only) and running hlds (counter strike 1.6). And its getting restarted after 6-7 days auto.

Config:
Xeon Processor
4GB RAM

What could be the possible reasons ?

Possible stuff I'd hunt for:

a cron job, if the restart is at exactly the expected time
disk quota, what is falling down? Why?
when the last update happened, maybe there's a dud piece of soft in there that brings the machine to its knees
desktop edition as server? maybe a real server platform is more suited (FreeBSD, Arch, the server edition of Ubunto, CentOS,...)

luck and happy gaming

Thor

Yes. I'm going to switch to server edition soon. CentOS or Ubuntu server edition is the choice.

Can you tell me that can I install CentOS 5.6 (x64) minimal from Centos Disk 1 only ? And will it require any lib packages to run 32bit hlds binary ?

Well...why run a minimal system? If that is a requirement, I'd go for Arch Linux. It only installs what you need, not what's on the menu - after the install, you're left with adding the stuff you need. I've gotten CentOS running, but I come from the RedHat corner of the universe.

Be warned about Arch though, a setup like that is not really for the faint of heart. You may want to read up the documentation first.

But...on the other side...just what's the hardware? Run

in the console (as Root) and look at the output, maybe an Ubuntu (that you seem to be used to) could just do the trick...you're capable of running 64-bit (I guess) so, punch is not the problem...

Thor

Yes, I'm familiar with ubuntu. So should I go with ubuntu ?.

Definetly. I've been distro hopping myself (RedHat-Fedora-Xubuntu,Debian-Arch) and it's been educational, but since you're running a server and the service thereon, sticking with what you know (for that) is the way to go, and if you've got a spare PC, experiment with that...
I've got some servers running, I only use on them what I know. No experimenting with those.

Thor

Yes thats true.