Here is the good news:
Companies that you work for cannot (according to the law of the land) divulge your salary. So no amount of background check is going to help there. They can just say 2 things: (a) Duration of your employment (b) Title. Some companies go a step ahead and ask you to give reference of your manager. Even then they cannot ask for your pay. So you have an air-tight case here. So all the above posts about the background check on pay were humbug

(I feel sad when people geniunely try to help but end up mis-informing).
Here is the bad news:
Most companies ask for your last pay slip and some smarter ones also want your last raise. So that way they know that you are not coming to them in May when you got the 20% hike in April. Forging documents for a few lakhs of rupees is the stupidest thing you can ever do to tarnish your career. Even if they get a whiff of it (say you are getting 5lpa as a s/w engineeer at Chirkut Software Services) you are jacked!! Your career can be ruined as it can even initiate a legal proceeding against you. If its your friends company and you can make things air-tight go ahead and do it. Most large companies will usually discount your previous pay if its extraorbitant from a small company. Their premise is simple "We pay X rupees to this guy who joined this company 2 years ago from college. We cannot pay you X + delta when you are coming in from another company and dont even have the same exposure to our company perspective and technology as he has". It is hard to negotiate.
Here is some positive news:
Companies pay people based on a variety of factors. Here are some:
(a) Uniqueness of skillsets - Getting someone who was worked on DSP (digital signal processing) is a lot more hard than some one who has plain vanilla Java experience. More like a demand-supply thing.
(b) Company policy - Most larger companies (TCS/Infy/Wipro etc) follow the footsteps of the PSUs. They usually have a band for which they pay only so much. So with 2 years experience they would put you as say Software Engineer Band 2. And at that level there is only so much you can get. There is very little room for negotiation.
(c) Fit - Say they are looking at someone with experience in the commodities derivative market and you have 2years solid exp working for a hedge-fund company with a certification from NSE. You have a good base to negotiate. This differs from (a) because in this case you do have an option of getting a smart bloke and train him.
(d) Urgency - If you fall in category (a) or (c) and the company is looking fast to hire someone they might stretch a bit to pay you a premium for that.
(e) Intangibles - Who would you define "leadership" or "communication" skills? So you meet this guy in an interview who is clean, crisp and has a personality of a talkshow host. You would want to hire him because you feel not only will he be a good brand ambassador he will also be able to motivate and work great in the team.
(f) Previous salary - This is more like a parameter against which they would want to peg your current salary. I mean they wouldn't offer you the job with a 20% pay-cut but at the same time no matter how good you are they would think twice before a 100% increase. Unless its a totally different job role or some which involves risk (say night-shifts) its your previous pay which is going to act as the barometer.
(g) Market standards - Most company HRs have a pulse of the market. They know what the competitors pay. They know where on the bellcurve they lie and its compensation is based on that.
(h) More than just take-home - Some companies pride in providing A+ facility which is more than just a number. Free food. Free cab service. Free trainings. ESOPs. These are accounted for in the "gross pay" but maynot show up on your payslip.
I could go on .......... but I will stop here
So ask yourself - what do you bring to the table? How would you sell yourself in an elevator pitch ? Saying that you have 2years experience in Java is not going to help you sell yourself. There are a million others from AP who are willing to work for a lot less. Once you are able to figure out your spiel you can convince the HR to go down your train of thought and make them stop at Moneyville
And please stop taking money as a criteria to guage how well you are doing in life/career. I used to earn about 84,000 p.a when I started my career - but what stood me in good stead (and what helps me negotiate a lot larger package now) is what I learned and what I did then. So my sincere advice is stop worrying about the 2.4lpa and 4.5lpa - in life that extra 5000bucks a month (which may seem a lot now) is just not going to matter. Focus on building a career.
Hope this helps,
Arun