Is it me or are the accents wrong?
Yes, the accent in 'tydzień' should go on 'ty' and here it goes on 'dzień'
Yeah, for me it sounds slightly odd too.
What's difference between tydzien and niedziela?
A major one. I'm afraid that you got Polish confused with Russian ;)
"tydzień" is a week, "niedziela" is Sunday. Yeah, it's almost the same as the Russian word for a week.