Hello, i'm brazilian too and work everyday with apple computers, therefore i had the same problem you are having now. Try these commands, they work on regular apple keyboards, but i'm not sure if they work on PC keyboards:

alt+e = (acento agudo)
alt+n = (til)
alt+i = (acento circunflexo)
alt+u = (trema)
alt+`= (crase)

I know it's really annoying to type that way, but you get used to it after a while. At least its cheaper than buying an apple keyboard and easier than setting up kext.

Also, try using alt key with other keys, like alt+8 gives you , alt+9 gives you (superscript "a") and so on...

BTW: the reason i'm replying in english is to be helpful to other people, non-portuguese speakers, showing the same difficulty.

I hope it solves your problem. Cheers.