Hi Forum Members,
Thank you very much to all of you for your responses. The discussion was very much fruitfull Here is the conclusion and summary of discussion...

Bit-Banged USB

1. Possible only with a high MIPS [atleast 10MIPS] micro that too will give low speed 1.5Mbps.
2. Devloping the driver and firmware will need considerable effort and probably I will get old my hairs will turn grey :) by the time I complete it.
3. One needs to get something called vendor number which is again very expensive.

Hardware USB

1. Option available are dedicated USB controller such as FTDI. A 8051 micro with built in USB support. If you don't have access to these 8051 micros with USB in them you can use some other micro such as microchip 16C745 / 16C765 solely for the purpose of USB your 8051 micro can send the data parallely or serialy ro this PIC which in turn will send it through USB.
2. You dont need to write firware USB instead a tiny code in 8051 with USB, 8051 with FTDI or 8051 with PIC will be needed.
3. No need to worry about writing the drivers.

I can't find 8051 with built in USB or FTDI in my local market. I can't import these FTDI since I don't have an import licence. I will use microchip 16C745 with an 8051 for implementing USB.

Regards,
Prhlad Purohit