1. If i purchased ALTERA USB Blaster ( Link attached ) then can i use it to program xilinx FPGA's
Not to my knowledge, each device manufacture requires their specific device for their device families, it primarily comes down to the software drivers supported by Xilinx, Altera, Actel, etc, software and the need for the device to support both JTAG, specialized internal analysis features specific to the manufacturer, like ChipScope, and a synchronous serial interface for programming external memory devices, like SPI.
There are third party JTAG software and associated JTAG devices which may in theory be capable of the task with various manufacturer's FGPAs, CPLDs, etc, however they are intended primarily for JTAG board level boundary scan testing and the programming devices being a secondary feature. The specialized boundary scan software and associated JTAG devices tend to be quite pricey,
JTAG Technologies is one such company. However, this would not alleviate the requirement to program SPI memory devices required to store the bitmap for volatile FPGAs nor provide the advanced analysis features, like ChipScope.
In the long run, purchasing the required devices compatible with each of the manufacturers whose devices you desire to incorporate into your designs would most likely be the most economical path.
There are numerous clones available which can be purchased at a fraction of the price of the genuine device from the manufacturer.