Thanks Michael,Kai,Rob and others for your help in explaining the issue .I have never designed the mixed 3.3V/5V systems before .I need one more suggestion suppose I want to use a buffer for driving Max232 as follows:

[Cygnal]------>[74HCT244]----->[RxD- Max232]
[Cygnal]<----------------------[TxD- Max232]

I feel the above is self understood and no explanation is requied .will there be any problem regarding the mismatch in the slew rate of power supplies, when the two power supplies are loaded differently ? Or is it insignificant .

Regards
Sanjeev