It is legal as trading forex is how banks hedge risk for importers and exporters. To learn about the legalities about foreign exchange trading have a look at Compass Markets
There is no legal recognition to Forex trading in India, but the Indian laws allow an Indian to send remittances of up to $25000 annual without asking for much of an explanation, so many traders are...
Forex trading is the trading of national currencies. In other words, the trading of money. The name Forex is derived from FOReign EXchange, which is the worldwide market that deals in currency...
By halaal I'm assuming you mean to ask if it complies with the Islamic law. Some forex brokers have set up Islamic accounts specifically for this purpose. They are know as Islamic or Swap free...