hi..
off late it has become increasingly difficult 2 make any serious money frm arbitrage .some of the very best arbitraguers are going through a very difficult time.I'll try n give u the reasons
1. it is very difficult 2 get a good 'seedha badla' (premium in futures over cash) these days.
2. with the advent of arbitrage softwares, it is very difficult 2 match their speed manually. if u decide 2 use a software urself, the broker would charge u more, either in form of higher commission or higher sharing ratio as he has 2 factor in the cost of the software.
3. nse is providing a facility for system trading 2 few of its members for 35 lacs annual fees wherein the member would be provided rack space 2 put his server close 2 the nse server in Mumbai, frm where he can do system trading. needless 2 say, his trades would reach the exchange faster than ur trades.
Only one form of arbitrage is still alive ,ie. nse to bse arbitrage becos sebi has not yet given the approval to use trading softwares for interexchange arbitrage. but u can imagine the kind of competition u'll face there. do consider these points before takin up arbitrage as a career.
hope this helps