Please help (domain issue)

[popasx]

Hi,I have installed xampp.I am going to set a LAN site.I donot want my site in internet.It will be only accessible via LAN.

But I got a serious problem.
Here is my network condition:
Here,I have got coneection through a network.Actually it is a university hall.we,200 student are connected through a computer(moderator) in each hall.There are 5 halls.So 5 moderator are connected to directly ISP.
When I go to "whatismyip.com" it says something like this "115.127.15.6".And it always and all time says this.Even I go to "whatismyip.com" from another computer(my friends PC on another room) it says "115.127.15.6".It seems from world,we all are known as "115.127.15.6".But internally we all have different IP.Here my ip is
"192.168.70.136".When I go to start>run>\\192.168.70.136,I can see the folders,i am sharing.Thats the connection condition.

Now the problem:
After installing xampp,i start apache and mysql.And I can see interface by going to "http://localhost" or
"http://192.168.70.136" or "http://127.0.0.1".When I browse from another computer "http://127.0.0.1" and "http://localhost"
do not work.Only "http://192.168.70.136" works.But I do not like this.Say i want "http://princeofpersia.live".when any user on our network(LAN) type in address bar "http://princeofpersia.live",they will see my site.But how can i do that.
Should I need a software to do that?
And buying a domain is not possible for me.And I can not consider it for some reasons.
1.The host PC is mine.(one PC)
2.This is a LAN gaming site.
3.Every single page is over 15MB.
4.Total space for webhosting is over 1TB.
5.Total system is non-profitable.
6.Main IP "115.127.15.6" remains same but secondary (192.168.70.136) one sometime changes.Say some stupid of us have started to use mine(192.168.70.136).Then condition get more worse.I need to change my whole site.My whole domain changes.So if I could manage a static domain like "http://princeofpersia.live",these problem eleminates.

This is my condition,please help.

[popasx]

ohh now it seems ok.I just installed "Simple DNS Plus" software.on setting i installed it as service.In DNS>request>all local IP address selected.On general,domain is in by default.(it neednt to be changed).In my case it is "princeofpersia".Then pointed browser to "http://princeofpersia".Then xampp webinterface appears.Even frm my frnds PC,it is ok.It seems
anyone on my LAN's TCP-IP who type in browser "http://princeofpersia",get my site.