Build version is, whenever  dev will be adding new features 
to the appliaction they will give new build to test. but 
software version is customers will change their 
requirements by that time they will change version name

Build version id means suppose after development they gave 
the build1.0 ok ag\fter that we will test it and report the 
bugs after fixing those bugs they will give build2.0 like 
this they will give n number of builds depending on the 
bugs fixed this is internal to the company only


Software version means IE6.0 is there now they release 
IE7.0 with some new functionalities after one year they 
will add some more functionalities and they will release 
IE8.0 this is software version

Thanks Nidhi an Laxmi for replying me the correct answer.
Now I get the clear difference between build Id and 
Software version Id.

Thanks all of u,
Especially Laxmi because I always get reply from Laxmi.

Thanks & Regards,
Samprati

Build is kind of an internal release without having any 
major change request from the client side.as they said 
above, there will be the plan for giving the new build say 
for an example twice in a month or something.. in that for 
our referrence we will give the build version number . 
Normally build version number should be 

XX1.0 ( XX is the short form your application)

But in the case of Software version , suppose u gave the 
software version as XX in .net 3.0 but in future they need 
an update version XX1 in .net 3.5 then its called an 
software version.. not like IE6 to IE7 thats something 
called an compatiable (upgradation )

Build Version: Application version, which is available in 
the testing environment.

Software Version: Application version, which is available 
in the client or customer or end-user environment.

Thanks, Suresh