You can use XR2206 function generator for sine wave generation. Use digital potentiometers using an 8-bit microcontroller to control the frequency and amplitude of the sine wave.
Added after 1 minutes:
There is also a very good article on Circuit Cellar FTP regarding designing of an inverter . I don't exactly remember the url.
That is true, but unfortunately the XR2206 cannot deliver 250 watts, nor will it tolerate 230VAC input for very long.
Some important specifications were omitted by prasanth9255: What is the output voltage of the inverter, and at what output frequency? If the output has same freq as input, must the output be phase locked to the input? Presumably the output is isolated from the input power; is this true? If so, how much isolation is needed?