chartset problem.. need help..
 

I have some spanish txt file.. on a computer i see the text well but on other computer i see different characters.. for example instead ó i see ó, instead í i see Ã, instead á i see á etc..
also, if i upload the file on my server i see the text with wrong characters..

what can be the problem and how can i solve-it? i think that may be a charset problem but i have no ideea how can i correct this :(