I have bought a laptop with 80 GB hard disk with 2 GB RAM. I want to keep two OS, Windows (15 GB) and linux ( 65 GB, likely centos)... to make the partition most effective I need some feedback on how much space to give to each partition... for linux ….. /var, swap, /opt, /usr, /tmp, /usr, /software, /, /etc, /home (please suggest if any other partition is also required), ………so on so forth….. among all these partition which are needed to be separate than root and which can be combined in root without any disadvantage….how much space should be given to each of them….my first preference is to save data in cases of crash than to have big space in /home….. as well as good speedy performance again have priority over home space…..

Who made the laptop, and did it come with any CD-ROMs? I cannot help if you don't tell me that minimum information. Also tell me what the CD-ROMs are. This would be very helpful.

Jham, please reread the questions as your requested information is NOT needed.

Now to the queston in hand.
If I'm reading you correctly you want to set it up something like this:

• Windows - 15 Gb
• Linux - 65 Gb
  with seperate "drives" for:
  
  • /var
  • /swap
  • /opt
  • /usr
  • /tmp
  • /usr
  • /software
  • /home

Ok very possible but really unneeded.
It is perfectly OK to just have one "drive" for the whole of Linux and run the required directories from the root of that drive.

Just one thing to bear in mind.
It would be best to allocate the largest "drive" to the OS you will use most often, so if its Windows then give that the 65Gb part and the 15Gb for Linux.
Windows is the major piece of bloatware here so give it the most space.

With you concerns of a crash, just ensure to take regular, off machine backups, to something like a cd or even another attached hard drive.