My wife saw the  SingStar trailers that comes withe the ps3 and she wants me to buy it for her, but i have no idea what the game is about and what songs are available, she doesnt speaks english so i need to know if i can download songs in spanish to. Please tell me what this game is about and how is played.

Well, it's a karaoke game. Unless you buy one of the regional Spanish ps2 games though, I think the main ones for the PS3 are all in English.
There are however downloadable Spanish songs - http://en.wikipedia.org/wiki/List_of_downloadable_songs_for_the_SingStar_series#Spanish
Provided you can register your credit card on PSN.

P.S. But songs are a good way to get into a language, one can sing without understanding (she can still hear the original voices, it's not completely instrumental karaoke).

i buy with psn cards purchased at ebay, anyway is there a regional restriction for the songs? if i log on to my euro account and down load a song can i play it on my main account? and how much does a song cost?

You can use songs between accounts on the console, but I think they are region locked to the region of the game on the disc (not sure, just most psn stuff seems to be that way and songs in particular need to be licensed).
So if you buy the US version of the game you'll probably only be able to play songs downloaded from the US store (which is okay because there are no EU psn cards and there is no JP SingStar).

Not sure about songs price anymore, it's been quite a while. But I think it was $1.99.

so there are 3 column on the right that says ES, UK, US does that means i can download the ones that say yes in the US column? from the US psn store?

Exactly.

Buy it for her and she can get you the trophies!