Beware: stepping up from S7-200 to S7-300/400 is not easy. The S7-200 is in fact a descendant from the TI PLC's, whereas the S7-300/400 are "real" Siemens PLC's.
The S5-90/95/100 families are also real Siemens PLC's, but these are out-of-date.
So, stick to the suggestion by Moggie and count on having to learn again when stepping up to the bigger S7's.