Greetings,
Questions: 1. Is it possible to install Koha 3.12 or 3.14 on CentOS 5.x?
No, it is not easily possible. Newer, supported (by the general masses for small amounts of free time) versions of Koha require Perl 5.10 -- and that's still pretty old. However, CentOS 5 (if I recall correctly) still only has 5.8. You would need to figure how to upgrade your Perl without busting the rest of the environment. I don't know how. CentOS 6 does have 5.10, but getting Koha onto CentOS is not the easiest of tasks.
2. I referred this post but not being able to get it to work. What are the packages which I should get before I start installing Koha into it. 3. apt-get does not work for me. I have wget installed but no dpkg as explained in this post. 4. I am totally new to VPS thing, where exactly should I copy all the files etc.?
There are different kinds of Linux variants with their own packaging systems. Debian and debian-based OS's (like Ubuntu) use apt-get. CentOS is not Debian-based. It is Red Hat based. You would use yum. However, you can't get an apt-get command, turn the word apt-get into yum and expect it to work. Red Hat and Debian do many things differently.
OS: CentOS 5.x 32bit Bandwidth limit: 500 GB Memory: 512 MB Disk: 20 GB
Lastly, 512MB?! Seriously consider 1GB at least. GPML, Mark Tompsett