It says on the back of the case that it supports only 720p. now in my parent's house they carry a rather old hdtv, which only supports 480p and 1080i.

question: would the game actually play on that tv?

Yes, according to posters on http://boardsus.playstation.com/playstation/board/message?board.id=ps3&thread.id=1543693&view=by_date_ascending&page=416

See how the image shows it playing in 1080p. If it does 1080p, it can do 1080i.

well.. question 2. do you think it will scale down to 480p or scale up to 1080i?

its coz the back of the box of uncharted also says just 720p, and when i tried it (on a rental) it scaled down to 480p.

aside from that, there are some differences between 1080p and 1080i...

coz i wanna make sure whether that tv can run it properly before i buy it.

That was then, this is now. It would scale up to 1080i.

Look at page 414 of the thread I directed you to. It is filled with people who are confirming that it scales up to 1080i. That thread is THE source on the matter. It is very well maintained and more reliable than the back of boxes.
http://boardsus.playstation.com/playstation/board/message?board.id=ps3&thread.id=1543693&view=by_date_ascending&page=414

Uncharted was released last year before the developers were providing upscaling abilities to their games. EDIT: The PAL version of Uncharted is 720p Only. NTSC Version does do 1080i.

EDIT: Always keep an eye on the following post since it is always updated:

http://boardsus.playstation.com/playstation/board/message?board.id=ps3&message.id=1543717#M1543717

thanks man! dogs do rule! i'm gonna go out and buy it now...

hey wait, will soul calibur 4 scale even if its PAL or NTSC?

I figured that you were posting back since you had bought it. I'm not sure. I see no reason why it would not. Uncharted is the only game on LeetFoo's list where there is a compatibility difference between PAL and NTSC.