do i need a travel adapter for a dell inspiron 1501 AC Adapter?

the input is 100 - 240 volts and in portugal they take 220 volts of electricity

First check with the manufacturer to make sure.
The plug for 220v is different from 120v but, you don't need the one that coverts 220 v into 120v those are more expensive.

You do not need a power converter, but you do need a plug adapter in order to be able to connect to the wall socket. You can find them in many places like Target, Brookstones, most luggage/travel stores, airport shops, etc. You can also buy them here in Europe.